I place my stat probe between the uth and the cage outside. This is how my AP cage was meant to be set up. They have a recessed area already cut out for probe placement. I can then place the accurite probe under the substrate. It's normal for your stat to be set to a higher temp to achieve your target temp inside the cage. My stat temp is set for 97, leaves the cage floor at 93, and on top of the substrate it's 88. You'll just have to experiment to what works for your set up. Different cage materials and substrates will play a big role in how efficiently the uth heat penetrates thru them.