Let's recap
>shortstack is body proportionsThis is very close to true, but does not quite work, as
>>280536918 and
>>280537157 have demonstrated.
As
>>280537474 points out, you know it when you see it.
So, it has to be a woman of a certain height and proportions, and of a certain level of apparent physical maturity, otherwise it becomes something else.
Additionally, I would like to suggest that the height has to be such that the eye-level is roughly equal with the male navel.
Also, there is the species consideration: shortstack goblins and yordles are more believable than shortstack humans: the maximal physical growth of shortstacks has to be such that the average human male towers over them.
Human shortstacks, like MHA's La Brava confuse this somewhat, but I think we're on the right track, here.