Flat_chested and the presence of boobs to determine gender is almost entirely left to human like creatures, and not feral creatures.

In the case of "canon" mlp images (aka feral) we tend to give body and head shapes more weight than we give the absence of crotch boobs, teats, or normal boobs.

So, again, it doesn't work like that.

Also:
post #376240 is a female looking pony with a penis, thus dickgirl. Tags reversed.
post #772816 has a male physique (square shoulders, only slight hips), thus cuntboy.