My quilt is over a top sheet and still creeps down a bit. I like my shoulders covered and the back of my neck (I sleep on my side) so I feel like I'm constantly pulliing the sheet and quilt up at night. 100%cotton sheets, 100% cotton quilt with cotton or wool batting, so, go figure. The quilt isn't over-long either. I make quilts whatever size they turn out to be...they tell me, I don't don't often get to do more than 'suggest' a size to them!
Jan in VA