Very good! Same idea I have. The bigger the area and cooler cold spot, the warmer the basking spot. I'm using vision racks with great air flow and under tub heat via heat cable only on a small portion so even though they do have a pretty hot basking spot, they are not obligated to go near it.

When I was using back wall heat on my 16 qt tubs rack, I couldn't provide a lot of heat. If I did 90 in the back, the coolest spot would have been 84 and torture my animals... Lol

Thanks for the response!