I learned something in my pattern fitting class that I would like to share. We are making a pair of jeans now. We start with buying a pattern and then making a mock up (called a sloaper) out of cheap fabric to try on. The instructor looked at my behind in my sloaper and said "We're going to have to take a tuck in your pants." I asked "why" and she said "flat fannie". Hmmm. I laughed. So this is why I have such a difficult time getting dressed and my $150 jeans have to be covered up in the back. I had to take my paper pattern and slice it across the back from within one eigth inch from the side to side, under the pockets, then overlap the tissue paper to take a half inch out of the amount of fabric in the middle of the butt.
I thought possibly this story could help some of you other "flat fannies" understand the why of the fitting problem. Hope it helps.
I asked the intructor about the pair of designer jeans I was wearing and she said they also needed to be taken apart and have the extra fabric taken out to fit properly.