Depending on what you are using for substrate, and how thick it is will determine what the surface temp will be. If you are using a wood substrate like aspen, etc... it should only be about 1/2 inch thick and no more than 1 inch. Jujst because the substrate is 84-87 on top, it may be 93 on the glass, which is where it should be. Remember, if you snake needs the extra heat it will move the substrate to get to it. Even with newspaper and paper towel, they will get under it...