Chapter 2: Proportion Passes & A / B / C Sets

Created by Sarah Choi (prompt writer using ChatGPT)

Proportion Passes & A/B/C Sets in the Mecha Concept Pipeline

Proportion is where a mecha becomes readable. You can have great detail design, great materials, even great rendering, and still end up with a mecha that feels “off” if the proportions don’t support the role, the genre, and the camera. Proportion passes are the deliberate stage in the pipeline where you stop thinking about parts and start thinking about mass distribution, gesture, and hierarchy. They are also the stage where you can move quickly without wasting polish on a design that isn’t yet structurally right.

A/B/C sets are the companion tool that keeps proportion work honest. Instead of presenting the team with three minor variations, you present three distinct options that represent different proportion solutions. The “30% delta” rule is a practical heuristic: if option B is not at least 30% different from option A in proportion and read, it is not a real alternative—it’s an iteration.

This article is written equally for mecha concept artists on the concepting side and the production side. Concepting teams use proportion passes and A/B/C sets to explore direction and secure alignment early. Production teams use the same tools to prevent drift, to scale a roster consistently, and to guide updates, skins, and variants without silently breaking the established silhouette spine.

Where proportion passes live in the brief-to-package pipeline

In ideation, you explore silhouette families and big gestures. Proportion is present, but it’s still loose.

In iteration, proportion becomes intentional. You refine the chosen direction by testing how the mecha’s mass and limb lengths communicate role and motion. This is where proportion passes do most of their work.

In finals, proportion is locked. You can still adjust micro relationships, but the silhouette spine and overall massing should remain stable.

In handoff, proportion is protected. Your package must communicate what cannot change so downstream teams do not “optimize” the mecha into a new shape.

Proportion passes sit at the transition between ideation and iteration. A/B/C sets are often used at the end of ideation and again early in iteration, when the team needs to choose direction with clarity.

What “30% delta” actually means

The phrase “30% delta” is not a measurement you take with a ruler. It’s a way to force meaningful differentiation.

A 30% delta means that the viewer should feel that option B is a different answer to the brief, not simply the same answer with different armor plates. The silhouette spine should shift. The center of mass should shift. The gesture should shift. Negative space strategy should shift.

A practical way to interpret 30% is to change at least three major proportion relationships at once. For example, you might change torso-to-leg ratio, shoulder width, and head placement. Or you might change hip height, backpack volume, and limb thickness. If you only change one relationship, you probably have a 10% delta.

The value of 30% delta is decision-making. Directors and stakeholders can see tradeoffs clearly: “This one is faster and lighter, this one is tankier and more stable, this one is taller and more imposing.” Without delta, feedback becomes muddled.

Proportion as a design system, not a style preference

Proportion is not “taste.” It encodes function and story.

Long legs and a narrow torso often imply speed and stride length, but they can also imply fragility. A wide torso and short legs imply stability and armor, but they can imply sluggishness.

High shoulders and a wide chest imply power and intimidation, but they can reduce head readability. A low-slung torso can imply stealth or weight, but it can reduce heroic presence.

A tall sensor mast increases scanning identity but increases vulnerability. A tucked head increases protection but can reduce personality.

When you do proportion passes, you are choosing which messages the mecha should broadcast at distance.

The proportion pass mindset: big levers first

A proportion pass is not a redraw of details. It is a “big lever” pass.

You treat the mecha as simple primitives: head block, torso block, pelvis block, limb cylinders, backpack block, weapon block. You exaggerate relationships and test readability.

You should be able to answer, after a proportion pass: what is the silhouette spine, where is the center of mass, what is the stance width, what is the limb length rhythm, and how does the weapon volume balance the body.

You can do proportion passes on top of a silhouette, on top of a line sketch, or even on top of a 3D blockout. The method matters less than the clarity of the changes.

Common proportion dials for mecha

There are a handful of proportion dials that show up in nearly every mecha project.

One dial is torso-to-leg ratio. This controls whether the mecha reads as agile, grounded, or heroic. A higher leg ratio tends to read as stride and speed. A higher torso ratio tends to read as power and armor.

Another dial is shoulder-to-hip width. This controls attitude. Wide shoulders imply power and upper-body weapon dominance. Wide hips imply stability and lower-body mass.

Another dial is head placement. A central head reads as character. A tucked head reads as armored and utilitarian. A mast head reads as surveillance and tech.

Another dial is limb thickness and taper. Thick limbs read as load-bearing and heavy. Thin limbs read as fast but fragile. Taper changes elegance and “manufactured feel.”

Another dial is stance and foot size. Wider stances and larger feet read as weight and stability. Narrow stances read as agility but can reduce believability for heavy units.

Another dial is backpack and shoulder pack volume. This controls silhouette and can imply power, propulsion, or payload. It also controls how the design reads from behind.

Another dial is weapon mass vs body mass. Some mecha are “platforms” for weapons. Others are “fighters” with integrated weapons. The ratio changes role read instantly.

You don’t need to change all dials every time. But you should choose the key dials that matter to the brief.

Ideation: creating A/B/C sets that actually help

In ideation, A/B/C sets are most useful when they represent three distinct answers to the brief.

Option A might be the safest interpretation: close to references, close to expected genre language. Option B might push a different silhouette family: different center of mass, different negative space. Option C might be the bold one: a distinct posture, a unique head language, or a non-humanoid variation.

The goal is not to show three random designs. The goal is to show three strategies.

A helpful way to build A/B/C sets is to start with a fixed brief sentence and then write three different “design thesis” sentences. For example: “This is a striker built for urban mobility,” versus “This is a striker built as a mobile gun platform,” versus “This is a striker built as a stealth ambush unit.” Those theses will naturally produce different proportions.

For concepting-side artists, this makes feedback sharper. For production-side artists, it builds an early record of what was rejected and why, which helps avoid the team drifting back toward rejected ideas later.

Iteration: proportion passes as structured exploration

Once a direction is chosen, iteration often becomes a tug-of-war between function and appeal. Proportion passes help you explore that tug-of-war systematically.

A productive iteration rhythm is to do “micro A/B/C sets” within the chosen direction. These are not new designs; they are three proportion variants of the same silhouette spine.

For example, you might keep the same general silhouette but test: a taller version with longer legs, a heavier version with wider hips and thicker limbs, and a compact version with a lower center of mass. These are still 30% deltas within the chosen cluster.

You then evaluate them against criteria that are tied to the brief: gameplay readability, animation feasibility, role clarity, and faction dialect.

Iteration also benefits from doing proportion passes at different camera distances. A mecha can look great as a concept sheet but fail in gameplay. Testing the design as a small thumbnail is one of the fastest reality checks.

Finals: locking proportions without freezing the design

Finals are where you lock the silhouette spine and proportion relationships and then let the surface design do its job.

A common failure is “proportion creep” during finals. As you add details, you unconsciously thicken armor, enlarge shoulders, or expand backpacks. The mecha slowly becomes bulkier, and the silhouette changes. This is why it helps to keep a silhouette overlay visible during finals.

In finals, proportion changes should be limited to small corrections: adjusting joint spacing for rigging, ensuring the cockpit scale is believable, or correcting foot size for stability. If you find yourself making large proportion changes in finals, it often means iteration did not resolve the big levers.

For production-side work, finals also need to include proportion standards that can be repeated across variants: consistent head size relative to torso, consistent shoulder width range, consistent limb thickness classes.

Handoff: protecting proportions downstream

The handoff package is where you encode “what must not change.” This is crucial because downstream teams will make adjustments for rigging, clipping, LODs, and gameplay readability.

A good handoff includes a clear orthographic set and a silhouette overlay. It also includes a short paragraph of non-negotiables. For example: “Do not change torso height, shoulder width, or backpack top profile. Maintain leg length ratio and foot size. Maintain head placement relative to collar.”

If the project uses multiple outfits, skins, or modular gear, you should also include “safe zones” and “no-go zones.” Safe zones are areas where silhouette can change without breaking identity. No-go zones are areas that define the silhouette spine.

For production teams, this is one of the most important uses of proportion passes: you identify early which relationships define the identity, so you can protect them later.

Production side: using A/B/C thinking for roster scaling

Production teams often need to create multiple units quickly: variants, upgrades, enemy classes, boss units. A/B/C thinking helps prevent a roster from collapsing into one silhouette.

Instead of making ten units that are all medium humanoids with different shoulders, you define silhouette families and ensure the roster covers them. You might have a tall-narrow family, a low-wide family, and a top-heavy artillery family. Those become your A/B/C families.

Within each family, you can still create variation through loadouts, armor kits, and surface language, but the family proportions stay recognizable.

Clustering matrices work well here, but proportion passes are the tool that keeps each family distinct.

Common mistakes and how to avoid them

One common mistake is confusing “detail variation” with “proportion variation.” Changing armor shapes while keeping the same silhouette spine creates fake options.

Another mistake is pushing every option toward the same “cool” proportions, often driven by a favorite reference. A/B/C sets are meant to resist that bias.

Another mistake is ignoring the camera. A mecha designed for close-up key art may fail at gameplay distance. Proportion passes should always include a thumbnail test.

Another mistake is failing to preserve negative space. As designs get refined, artists often fill in gaps with armor, losing the original readability. Keep a silhouette overlay to protect negative space design.

A practical cadence from brief to package

A practical cadence is to treat proportion work as planned checkpoints.

Early ideation produces three A/B/C directions with real delta, presented as silhouettes or blockouts.

Selection is followed by a proportion pass sprint: three proportion variants within the chosen direction.

Once proportions are locked, finals proceed with silhouette overlay and periodic distance tests.

Handoff includes orthos, proportion notes, silhouette overlays, and safe/no-go zones.

If the project is large, the same cadence repeats for each role class, using shared proportion standards per faction and per family.

Closing thought: proportion is the fastest path to clarity

Proportion passes and A/B/C sets are not extra work. They are how you prevent expensive rework later. They create meaningful choices early, they clarify tradeoffs, and they protect the identity of the mecha as it moves through iteration, finals, and handoff.

When you learn to treat proportions as a controlled system—torso-to-leg ratio, shoulder-to-hip width, head placement, limb thickness, stance, pack volume—you gain the ability to design quickly and communicate clearly. And when you enforce 30% deltas, you give your team real options rather than illusions of choice. That is the heart of a strong mecha concept pipeline.