When it's half a foot or more difference (my own wild estimate, there's probably a measurable ratio somewhere) it appears to have a glaringly obvious effect. I weigh about 2.5 to 3x what she does, yet she has no problem moving me, due to her centre being much lower (e.g. a hip check destabilises my leg). Stiffening my arm merely gives her a nice lever with which to move me. If I resist otherwise, she changes direction, using my resistance to move me into the technique.

I know what you mean! I had the pleasure of watching at a gassuku about a week ago. The smallest person threw a mammoth enough to clear several meters! It was like the principles needed to be greatly emphasised. Is lack of height an advantage then? A further thought, could we view relative height as a weakness, an ad for ways by which uke can be overcome? Like other concepts this seems so counter-intuitive yet plausible at the same time, quite opposite to popular culture and common practice.

One of my instructors, at 4'10 to my 6', is naturally low enough to put me off balance almost immediately when I grab her wrist. The initial movement for things like kotegaeshi, kokyu nage, kaiten nage etc is nearly enough to topple me as she moves. My choice is either bend at the waist or squat, if she takes things lower, and both end with me flat on the floor.