I just picked up a Reptile Basic Iris Sweaterbox Rack-32 Qt w/ Back Heat. This is my first time using back heat and I am having trouble getting the back of the tub up to 90. My thermostat only goes up to 105 and is clicking off before the tub temp reaches 90. I know the thermostat is working correctly because I have a thermometer probe on the flexwat. My room temperature is 81.

Does the flexwat really need to get over 105 to transfer the heat to the back of the tub?

thanks