I am struggling with a pants fitting problem. When the pants drape nicely back and front I get a large wrinkle from my backside (see drawing) along the inside of my tight ending on top of my leg as soon as I bring a leg forward to walk or sit down. When I sit there are many wrinkles from the crouch angling toward the outside of my knee across my tight. The only way I have found to reduce the wrinkling is by making the crotch seam shallower. This however adds fabric that billows below my behind when I stand straight. It also cuts (slightly but) unattractively between my buttocks.
None of many articles I read on pants fitting cover this. It seems pants I purchase have a varying degree of the same problem. Is this unsolvable or is it just my shape?