When I roll my quilts up, I lock the rail down, then do a "test run" with the laser, and the machine not running with teh presser foot up. I can watch the needle area and make sure the new row nests into the previous one without overlapping or leaving too much space. If I need to, I stop the machine at one of the upper "nesting" points and roll the quilt up or down to get the spacing right. The only problem I have is when I get to the end of the quilt and have to try to adjust the spacing to end the quilting on a full row.
Darren