Achieving proper temperature gradient thru several inches of substrate? (TL;DR)

[BonnieBallPython]

First, if your snake is hanging out on the cool end (75*) most of the time, it suggests that your snake is too warm, so I'm wondering how accurately you're taking the temps. inside the enclosure- I just want to make sure you know that you cannot rely on what a t-stat is set to, you need to verify all temps. independantly. Most here use a "temp. gun" to read the temps.

UTH- is usually low wattage- yours is 24 watts- that CANNOT penetrate thru thick substrate- you need less than half inch of substrate over the UTH to be effective, and also, IF your UTH is not vented (installed correctly per instructions), you run the risk of it overheating & shorting (could cause a fire) so for safety, please re-think the amount (or type) of "insulation" (aka "substrate") you have over the UTH.

If you must have thick substrate, you'll need to heat (using various options) only from overhead.

I have 4 different thermometers in the tank. 2 came from a pet store, advertised for reptiles; 1 with a humidity gauge. The other 2 are cheaper indoor hygrometer/thermometers I bought online. They are all consistent with each other within a degree or so, when put in the same spot. Otherwise, I probably would buy a temp gun.

As for insulation, the bottom part has good space for airflow and I keep the substrate low above the heating pad, about 0.5-1 inch. The wire is not pinched and I am constantly checking the temps in a day.

Thanks for the rest of your response as well. I will probably end up ditching the pad I bought altogether.