I've been taught (right or wrong) to avoid putting the seams at the common fold. I'm told it weakens the seam to be folded and unfolded, and that does make sense to me. It would depend on how the quilt might be used that would determine how I did the back. If you know it's not going to be folded/unfolded a lot, seam placement wouldn't be as much of an issue as with one that would be in and out of use.