Temp and substrate questions

I have a rack system and have been battling trying to figure out why i cant get my temps even. I have narrowed it down amd am very close to gettig even consistant temps accross all 8 tubs. However for some reason i have one tub that is getting hotter then the rest. Connections are good. So not sure why. But it has hot spots on the substrate arround 95.. But most areas are 90 on the hot side... Will this be bad for one tub to be this hot??

Allong the same lines as the above questiom. Curious how u guys set ur temps to deal with substrate.. My flexx watt must sit arround 108 to get roughly 88-91 in the tubs.. But it also varies based on subatraight thickness. I have some girls that push down to the plastic and others that dont.. The substrate insulates about 10 degrees.. So i have begun to thin out everyonea substrate.. What does everyone do to battle this?

I use paper towels and have my VE set to 96 and its between 91 and 93 in all seven tubs

I know in my RBI rack the top two drawers are always slightly hotter than the ones underneath, I've pretty much decided it's because heat rises.

As far as the temps, I have my herpstat set to 103 to maintain 89-90 degrees inside the tubs. I use a temp gun to check the temps. It takes some trial and error and common sense. There is about a centimeter between the flexwatt and the tub, which is why my temps need to be set higher to get 90 degrees. If the tub sat directly on the flexwatt it wouldn't have to be set so high, maybe 94-96.