Two exact tubs problems with temps

Is there any reason why the one tub would be a few degrees lower than the other i havr o tubs set up the same waybwith the sam UTH and hooked up to the same thermostat but the one that is empty right now(waitng for my spider) is always about 88-89F while the other is 92-93F could it be differences where or how i put the probe for the thermometers?
THANKS FOR LOOKING!

probe placement is a factor and so is a faulty heating pad not heating up evenly. 88-89 ur snake will live comfortable in those temps.

Thanks so much just wanted to make sure *PHEW*