I have removed the bottom two rails. They get in the way of my legs when I sit or try to change a bobbin. So I just use the backing bar and the uptake bar thru the machine head.
This view is of the frame with the quilt ready to be worked. It just drapes over the edge. This is a small kid's quilt, but I do larger quilts like this as well. It works just fine unless DiNozzo lays on everything underneath. He is the quilting basset in the window seat I had to make for him in the studio.
Here is the view of the quilt hanging over the frame edge (backing bar) and ready to quilt. This is the dining room. Like that carpet? I did until I had to find things I dropped on it!