Just to clarify - Do you have a 90deg hot spot that you drop to 86deg at night (even though you said you don't cycle them), and your ambient temps are 83-85deg, or are you heating the whole room to 90deg and letting it cool to ~86deg at night? Or am I more confused that I think I am? If you have a 90deg hot spot and 85deg ambient, then you really aren't providing much of a gradient. Drop your ambient temps to ~80deg at all times and keep a 90deg hot spot.