Current distance from the heightest basking point in hot area is something about 10-11 inches (30cm). Cold area though has no direct vertical UV lights: enclosure is "divided" by 2/3 + 1/3 to provide a cold and hot areas.Your UVB is a T 5? If so the distance needs to be 12- 15 inches directly above him -- NO back wall if so -- for a T 8 distance would need to be 6-8 inches directly above the basking decor
Do you think 1-2 inches make a big difference in UVB for the dragon?
He controls (I think at least) that: sometimes he likes to spend a day in a cave and more oftenly he likes to seat in hot area.