I would be concerned that this is too much heat in a small area. Tubs are such a small surface area that a lamp often produces too much heat. Did the thinner layer of substrate help? I don't like seeing over 94º anywhere inside an enclosure unless it is over head ad then not more than 100º. Less substrate should correct the hot side issues. I usually have only a small bit on the hot side. Less than a 1/4 inch. You might find that a towel folded on top of the lid to help some. IR guns can only measure surface temps BTW. When it gets quite cool out you may find placing a box around the tub so it is 6-10 inches larger one side open (box turned on its side) and adding a heating pad on low to the 'back' or ceiling' of the box will add to the air temp inside the tub. A dark blue bulb might as well but a dimmer would likely be needed.

Tubs simply do not have good insulation. Currently figure something out to get the right range when the snake gets a bit older and bigger close to adult size if you still have a single snake I would strongly suggest a 'reptile' enclosure they are designed for the purpose and usually are the easiest to maintain.

I feel like such a sh** pointing out out things like this but so few actually mention that temps can be hard in tubs located in cooler room temps. I am sorry for that. I run a rack in a cool room and it takes heroic efforts to keep it correct and stable. The PVCx enclosures I have look great and better yet are easy to heat efficient and do a decent job of humidity. It might be an option that will fit your needs in the future.