I have been longarming for 13 years and was never able to float my tops without them drawing in too much, leaving the bottom border with waves. I find I have much better results when I attach the top of the batting to thetop of the backing with a basting stitch while the horizonal channel lock is on. Pin the quilt top along that basting line and pin the bottom of the quilt op to the bottom roller. Measure the width and baste each side with each advancement. This works for me.