I have two 20 gal long tanks and purchased the Zoomed UTH for 10-20 gal. I've already set them up and now my concern is that I may have gotten one size too small? It does heat easily to the correct temp using a rheostat but it covers a small area of the tank and only heats that part. I made sure the warm hides are over that area. Is this going to work or should I try to peal them off and get the next size up to cover more area? sigh . .