Well yes and no, the ankle shouldn't be smaller than 90° !!! This is very important bc of your knees! If you want a better butt, use weight, do a squat workout but 100-180 "normal" squats a day are enough ! I did it and i'm happy with the result...pictures
Yeah everyone is spot on here lower the better as long as you have good form, if you are struggling to get lower you can grab a weight hold it out in front of you and use it as a counter weight
Actually I was a little wrong I have been enlightened and here is a study on why people squat differently http://themovementfix.com/the-best-kept-secret-why-people-have-to-squat-differently/# now don't get me wrong one should try and go to their full range of motion but arse tk grass squat may be anatomically impossible for a particular person same as narrow and wide squat its a great little article.