94 is a liiitle warm. I would shoot for 92 under the paper. If the snake is laying on the paper, it will probably let the heat pass through the paper to the snake. I find that my snakes move the substrate all the time. More often than not they are laying right on the plastic so it's good to make sure that spot doesn't get too hot.

Adjusting your rack can be a little tricky. I wouldn't worry too much about the temp difference above and below the substrate as long as you are getting a good hotspot below the substrate. If it was a thick layer of aspen or cypress mulch then I would be more concerned with the temp difference.

Hope this helps!