I think your appraisal of the conceptual differences between "full" and "empty" are on point. I think the question is conceptual because the matter is not: i.e., however defined, when we take steps, (all) our legs alternate in function.
Ther's no doubt that the leg that is stepped upon carries the weight. When both are stepped upon --i.e., when we stand-- both legs carry our weight. Here, though, I am interested in the way that the 90/10, 80/20, 70/30, 50/40, 50/50 and even 0/100 conceptualizations come into play. I mean, only the 0/100 formulation seems to satisfy the idea of absolute fullness or emptiness. Yet, even then, we know that those who advocate that idea also have to alternate their legs when they move.
I know that, for example, Wushuer is familiar with the 0/100 concept. I wonder whether that means that there is no "shifting" of the weight. Anyway, my point there is only that these questions are about conceptualization, not actuality.
Audi, I also wanted to address some of what you say about the Sunzi.
"In other words, Sunzi sees the opposition as one of black and white ( represented grammatically by “Heibai”), where grey is disregarded or not allowed."
I think that Sun is not being philosophical, or arguing the theory of "emptiness" and "fullness." He is approaching it from a strategic and tactical point of view. Every enemy/fortification --like every thing-- has full and empty (i.e., strong and weak) points. That is an absolute, in the sense that there is always a "strongest" and a "weakest" point: Not, as I think you suggest, that there is a point that is either totally full or totally empty. Indeed, as I read Sun, he is saying precisely the opposite of absolute fullness or emptiness. For example, he says, does he not that "intelligence" (which is what I think Jerry was arguing first: i.e., the ability to distinguih full and empty) makes all absolutes relative. For example, one can turn an enemy's strength into a weakness or, and this might be applicable to tcc, one can turn one's weakness into a strength.
Anyway, hope you all are having great New Years,
Despite this, I find an opposition of “relative heaviness” contrasted with “relative lightness” (represented grammatically by “zhongqing”) much easier to fit into Shen’s description."