Unless your skink is having issues (...you have an IJ, right?), I wouldn't worry terribly much about the numbers. Make him a little enclosed hide with some wet moss in it and place it on the warm side --see what he does. If he rarely ever uses it and is having no issues with shedding, then I'd say the amount you're misting the substrate is just fine.
Keep an eye on his toes for any cracks and/or swelling, and on his eyes for any discharge/crust.

Breeder and keeper of Meraukes from 2010 to 2022.