Glad you were able to do the salt test and find out the % difference. Usually, it's not that drastic but definitely good to know.
Yes, the CHE will suck a lot of the humidity out but don't get too worried about that. If your BP is not in shed, the humidity isn't as important as the temps. Once you observe your BP going into shed, you can either bump the humidity by misting once a day with a spray bottle or you can create a humid hide with sphagnum moss. The moss will also act as an abrasive substance to help your BP shed.
And don't worry about losing that BP. Breeding season starts right about September so there's going to be a lot of BPs that are going to be available by the end of the year or early next year.