hmm. re-examine the temps his cage is currently configured to and compare that to the temps recommended by NERD's caresheet; how big/small is the variance?

so far, you mentioned:

1) no mites. good

2) "looks healthy"; I will assume that you checked him for dehydration using the info in the link I posted earlier. good.

3) how often does he pass wastes? if regular, good.

4) kinda late question but when was his last shed? based on my experience, my retics and ball python usually shed on a monthly basis.

At the top of my head, I can guess that his "excessive" soaking is due to any of the following:

1) heat in cage is too high

2) getting ready for shed

3) he's a pseudo beach/pool bum

4) (sorta related to #1) his hides are situated in rather "hot" areas