One question though, my UTH is stuck to the bottom of my tank and I have the bro be underneath the tank. Is this not a correct way to set up? How can I fix this if the mat is already adhered to the tank?
You can carefully peel the mat back but you may damage it.
The problem with having the probe under the mat instead of between the mat and the glass is that cold air (a/c) can make the temperatures fluctuate more.