I'm a red foot guy, so for us, it is forever and always at 80%. I've read some of Tom's things on Leo's and sulcatas and it sounds to me like they always need a nice humid place to go to. In the wild they dig their own burrows and that gives them a good humid place for them to go. So long story short, the answer is, they should always have at least some place to go that's always 80% or greater