Low to mid 80's on the cool side is correct. This is where a thermostat would make a really good investment. You could put a second UTH on the cool side and set the thermostat to 83 degrees. It would be perfect.

That said you could do the same thing with a rheostat and a digital thermometer, it would just have to be monitored and manually adjusted if needed. Also, the UTH on the HOT side should be on a rheostat as well, some of those things can get really hot!

In my opinion thermostats are just as important as the enclosure when keeping a ball python. Proper temperatures are critical to their health and well being.

-adam