Jhaskins..... I have mine attached below the tank, between the mat and glass as well. I've seen others do it differently but this seems safest. To ensure it doesn't get disrupted, we taped it at two points... At the edge of the mat and just up the side about an inch. This seems to stop any additional airflow as well, which can prevent accurate readings and control.

Seeing others attach it under the subterate inside the tank, I found myself wondering if I was doing this wrong as well. Temp is set at 91, the hydrofarm thermostat is my best purchase yet. Looking at foggers now to help with humidity.

OP: Good luck Hun, I was less stressed out bringing in a 7 week old puppy than I am with getting my Naginis tank at optimum temps etc.