Pandora3d
What type tank are you using?
IE: Aquarium or pre-manufactured reptiles enclosure
I ask to determine if the pad is sandwiched between the glass and the surface the tank is placed on, or if air flow can occur under the tank.

Having a pad directly under a substrate with no drainage layer will cause the soil to dry out quickly, requiring misting for humidity to be done more often.
Are you using a drainage layer with this setup? If so, is it normally dry due to the placement of the UTH?