new set up ambient temps.

Hi Guys,
Just got my first snake, a ball python. I keep the temperature in the house at 65 degrees, so I have two heat pads (under tank ones) connected to individual thermostats, one on the cold side under the hide spot set to 80 degrees, the other on the hot side with the temp set to 90 degrees. The question I have on this is the meter that measures the temperature and turns keeps the hot pod at desired temperature should it be above,in the middle, or below the substrate?
The ambient temperature in the cage is about 74 degrees, I added tape to the top to cover most of it going to see if this brings the tempt of the air up, if not should I just get one of those thermal lights?

Thanks for your help, Sterling.