Made some small edits on the OP Highlighted in blue text, I didn’t spend much time on it really so if there is anything else I should edit/remove feel free to let me know your opinion but this is basically my opinion on what could still possibly be done now to solve the problem on the Female Miquo'te, without adjusting the but/rear at all.
Because the female Miquo'te has been changed so severely, re adjust the tilt of the pelvis so the back is straight "Not on an odd angle" could be enough to make the Female Miquo’te model look normal again.
The odd angle and forward tilt causes the concave look, perhaps this would also be enough to make the rear look less tiny as well because it wouldn't be weirdly tilted so far forward