@jokerxhisoka I say "theorizing" but mean "a couple of posts said that might be what's happening" and it sometimes pops up when people mention Yamada's booba.
Sometimes I think it's a matter of just some of of the instances where they look bigger than we expect, they're in motion and being thrown away from her torso for a moment. The mangaka being a woman, she might well understand the physics of boob bounce and shift better than the vast majority of dudes. I know there was a more recent piece of extra artwork that showed her relatively still and in lighter clothing, and she didn't look nearly as stacked as some art makes her seem, and I suspect it's a matter of physics and Norio understanding how it plays on boobs better than the average shonen reader.
Like there was someone wondering what was up with her boobs in one panel where she was wearing her coat, when, to me as a person who actually dated a stacked (specifically a short-stack) girl for awhile, noticed when she wore big wool coats like that (specifically a peacoat- we coincidentally had kinda matching ones, her's was purple, mine was traditional navy blue), the folds of the coat do stuff like that. Specifically, I mean page 10 of the last main chapter, #58...