quiltncrazy,
I have a lap frame that is 18". When I get ready to go to bed for the night, I looses the frame a little bit...this prevents leaving hoop marks. I get the fabric in pretty loose. It won't stretch the fabric, I haven't had a problem with stretching on one of my quilts yet. If you leave a little give in the hoop, you'll be able to rock the needle and have an easier time to get the needle through the fabric.