Anyway, the rationale for my questions is actually pretty simple:

#1) Some robots have weapons--see Getter Tomahawk--that aren't used built-in. Would these be individual parts, or a subset of whatever they're composed of? Particularly, there's the cases of "the weapon is part of the body", "the weapon is stored in the body", and "the weapon is basically picked up".

#2) Without some sort of template for size, it's hard to work out where canon robots are meant to fit except on the fringe cases. xD

#3) Based on the above, if size 2 is fixed at some point but you can't buy yourself smaller, some canon robots are locked out. Which would eliminate one thing I've been thinking about. Hmm.