Specific heat mat question that is driving me nuts !!!!

[Mikeyv2009]

So I recently just got my first snake. A baby thayeri kingsnake and I want to make sure I am doing everything right for it to be healthy and happy. First let me explain my setup before asking my question. My.snake is about 10 inches long right now she's in a 10 gal tank for the time being. I have a hide set up on each side of the tank , Aspen bedding for my substrate with a repti therm heat mat under the tank on one side ..it's connected to a hydrofarm thermostat with the probe placed on the glass inside the tank under all of the substrate where the heat mat is it is currently set to 86°f. The ambient air inside the tank is 75-77 degrees according to my digital thermometer. My question is do I have to turn up the heat mat hot enough to get the surface of my substrate to 81-86°? Because right now the surface is only reading 77°. The snake burrows down into the substrate to get closer to the mat which I placed some newspaper over so she doesn't come in direct contact with the glass ...my fear is setting the thermostat up to like 95° or higher to get the top of the Aspen warm and risk the snake burning itself if it chooses to burrow to the bottom. First time snake owner and just trying to learn !!!!