Rack system temp question.

Good day all,

I will explain set up and then ask question.

*4 level C-serpents V-15/V-18 rack
*3in 10w belly heat flex watt
*1st Herpstat 1-probe taped on flexwatt directly
*2nd Herpstat -probe inside empty tub taped to hot spot for accurate hot spot temp.
*Temp gun
*new substrate Aspen Sani-chips; old substrate Aspen shavings

Alright now for the question... Sorry I dont know how to explaining it without being complicated.

I am confused about hot spot temp. I have set up my second t-stat taped inside an empty tub to read hot spot surface. Since I have done this my hot spot has hit the correct temp where I should be for my hognose snakes 90 degrees (92 at most). Now after i switched over to sani chips, the substrate has actually stayed in place over hot spot without bunching up like aspen shavings. So when I did have aspen shaving I would use my temp gun to get reading of each tub and got same temp as my t-stat. Now that I have made the switch to sani chips I have used temp gun to read hot spot surface under substrate and have gotten temps of 96 degrees. So at this point i decided to to ad substrate(s-chips) over probe to compare reading and it is accurate 96 degrees. Am I doing something wrong? Should I bring down t-stat to get a 90 degree hot spot with substrate over probe or should i remove substrate and get reading from that? And just to be clear the t-stat inside tube is not connected to my flex watt. I'm using a separate herpstat to control temps. Once again sorry for my explanation.

Thanks,
Dave