From what you are saying it seems like your husbandry is spot on. When I first brought my boy home he spent 95% of his time in the cool side hide like yours. What I got with a little research is that each snake is an individual. Some prefer the hot side and some prefer the cool. My snake now takes a trip to his hot hide once in a while but still prefers his cool side most of the time.

What are you using to get your hot side temps? That can make a huge difference. If you have a digital thermometer with a probe undee the hot side hide your OK. If you are spot checking the substrate and getting 90, it may be 95 ot higher under the substrate. This was an early delema I ran in to.

Good luck.