In my experience when a cham is sleeping in different places each night, it is because all the lights go off at once and surprise the cham - so they basically go to sleep almost whereever they were when the lights went out (this is often what causes chams to end up sleeping on the mesh walls overnight).
There is a technique that works well to solve this problem. Zerah Morris referred to it as 'providing cues' that night time is approaching.
You simply turn your heat lamps off about 30-60 minutes before you turn off the UV bulbs. The chams then get alerted that night is approaching so they start making their way over to their favourite sleeping spot. By the time the UV lights go off, they'll be in the right place, ready to sleep.