What's your substrate depth? Increasing how much substrate you have, and maybe adding some top soil to the cypress mulch, could help with the humidity. That way it'll take longer for the moisture in the substrate to evaporate, and with your CHEs going, the top layer should stay pretty dry.
The substrate is about 2 inches deep.
So you would recommend adding something more humid to the cypress mulch (and/or adding more cypress mulch)?
Male Ball Python (Bumblebee het 100% Clown) - Friedrich
Female Cat (unknown heritage, was an orphaned kitten) - Shirley