he may be moving when you aren't looking. Keep that in mind too. If the two hides are identical, it shouldn't be an issue.

Dont turn down the UTH at night, young snakes don't need this and if it goes too low he could get sick and get a respiratory infection. If the UTH is the right temp (hot spot of 90-94ish) on the hot side, he can't get burned. This is the reason thermostats are so highly recommended.

Did you say what your enclosure temps were? (cool, warm, ambient and humidity) and what you were using to measure them? Perhaps the enclosure could be too cold overall and that is why he is staying on the warm side if he truly isn't thermoregulating.