The Fabrifast system is a dream...after you insert the leader into the crevice, you can move the leader back and forth. As to using the backing fabric directly on the rail, nothing wrong with using extra backing. You won't need much. If you wanted to check the tension first...just allow a bit extra, that's all. Or you can sew a strip of muslin to the backing and use that as the leader. Do your own thing, smile. You do need to use the leader for the bottom edge of the quilt backing, though.