you could put something between the tub and the flexwat to get the temps where you want them. one thing that i have learned in life is that no 2 things are never exactly alike no matter how much they look alike. i have 3 pieces of 11 inch on one of my tanks and all 3 read a couple degrees diff. i just run the hotest on one end and they get cooler as they go to the other side creating my temp diffs in my tank.