When I first started with my Voyager 17, I had the thought that if I had the side tensioners tight, the quilting would be "flatter". I found that yes, inconsistencies in the middle of the quilt might be flat but the edge of the quilt was sometimes wavy. If I have no border, I stay stitch the edge and when I have a border/borders the outer most border is always on the length of fabric if I have enough fabric to do so. I now "float my top", basting the edges tog before each pass and I do that before tensioning the sides.
It is all a learning process - there is so much to learn and remember - it takes a while. Good luck with your machine!!