I'm in the process of building a 7 shelf, 28qt rack and can't decide if I want to heat it with 4" or 6" THG heat tape. I know a lot of people use either 3" or 4" but I was thinking that the 6" would obviously allow for a greater heating area and thus make heating the tub easier. My ambient temps will be maintained using a radiator heater so this tape is for a hot spot only. What do you guys think, is 6" too much?