Well I took my altered #5 fitting pants and changed them again. I removed the back crotch extension and then I scooped out the back crotch curve. This is what it looks like. The lower seam line is the new one.
Here are the results:
While it helped with the wedgie it worsened the diagonal wrinkles from cheek to hip. I prefer the first alteration I did - flattening the back crotch curve. So I will take this knowledge with me, back to the drafting table (my computer). And hopefully soon I will have drafted the perfect jeans.