iridescent_slime said:
Whether it's giantess or miniboy, size difference still applies in circumstances like this. I'm not saying that between_breasts size_difference is enough on its own to make a person between breasts tag unnecessary, but it's still a useful tag combination.
size difference is a bit of a problematic tag at this point since it seems a lot of taggers completely ignore the wiki definition and use it for "natural" differences in size (like an adult with a child). I think it's in need of some massive cleanup, but that probably should be the subject of a different thread (to see if the wiki definition is even agreed on).
Even if the tag is cleaned up, though, there will also still be images like post #297458 and post #1837303 where there is a size difference but something besides the smaller person between breasts.