Okay to clarify. ThermoSTAT probe should go outside the tank on the UTH which should also be on the outside of the tank.

The thermoMETER probe should be n the inside of the tank UNDER the substrate. You want to measure the hottest point the snake can get to. If you measure on top of the substrate, the temp underneath could be high enough to harm your snake. They can move the aspen out of the way if they need to get to more heat.

I also agree that you should ditch the astroturf. It is a breeding ground for bacteria and is impossible to fully clean. Stick to disposable substrate.