With this statement I am guessing the humidity reader (vented area on the bottom of the unit) is in the or on top of the substrate. If so this is your problem.
Also to help your worrying add 2 extra hides on both the warm and cool side. Fill with wet paper towels or moss to add a humid hide. Add 2 on both sides allows the animal to not make a choice between cool, warm or humid allowing both humid hides on cool and warm sides.
I would also like to add that I keep my animals as HIGH as possible in the time they eyes go blue until shed day. Remember high humidity without condensation doesn't cause RI's but low humidity does.