need some help with temps might have a bad uth

[herculies]

I'm using a glass critter cage with a screen top covered with foil then duct taped with a 2"x3" hole for ventalation and enough room cut out for lights then covered with saran wrap with 1 1/2" of aspen

cool side on top of substrate is around 79-81 during the day, night drop to 73. added lights and stays around 77-79 at night
hot side on top of substrate is 86 and can drop to 83. 1 time it read 80 but after i added lights never seen it yet
my temp probe on the glass inside under substrate read 91-92 which is where i got the thermostat set but moving to the top it reads 89
it recently shed it wasn't good but not terrible i stuck towels over where i put the lights after taking the saran wrap off to bump humidity to 60+% after 24 hrs a bit of the head was still on it just the nose and the tail was also a little above the vent i think it's called that (where it poops) but a 3 min soak and a run through a washcloth it was off
could my uth be bad or do i need to switch substrates?

[The Serpent Merchant]

Your substrate layer is too thick, for a UTH to work properly the substrate layer needs to be very thin, ½" thick or less.

[NYHC4LIFE8899]

My substrate is that and my guy still burrows and lays directly on the glass,due to that,I leave the UTH lower so he don't get burnt but stays warm,he seems happy