It's all scale with IRL shortstacks.
On a tiny under 5" chick with her looking way too big for her frame 8DDs or 8Es (Aussie sizing, dunno what US use), the exact same size boobs on a normal height 5"5" chick would be like 10D/DD or 12C/D, not quite as impressive cause of how bra sizing works and the scale up in (non-boob) chest circumference, but the whole same size boobs on smaller body thing is still epic even if the boobs aren't objectively that big.
Anime/manga proportions are unrealistic at the best of times so no point bringing that up, look at the completely absurd waists on most drawn women, there's like spine and no room for internal organs