Specific heat questions for new set up

I have a recently set up enclosure. I do not have a snake in it yet. I will be getting my first BP in a couple weeks.

I have an Exo Terra glass enclosure 80% of the screen top is covered by my RHP or aluminum foil. I also have an under tank heater. Both heat sources are controlled by a herpstat2 thermostat. My ambient temp is holding nicely at 80. I am using a mixture of Eco Earth and Reptibark, the substrate is 3/4 to 1 inch deep.
Two questions

1 I am having to mist the enclosure 1-2 times daily to keep the humidity at 60% it drops to about 50-53 without the misting, is misting twice a day a problem?

2 The thermostat probe for the under tank heater is between the pad and the glass on the outside of the enclosure. I have it set at 109 degrees currently and I'm only at 85 surface temp on the hot side. I move the substrate and the glass is only slightly warmer about 90. What is everyone having to set their thermostats at to get surface temps to 90? I am concerned to set it too high in case the snake moves substrate and ends up laying on the glass. I am measuring surface temps with a good quality infrared temp gun.

Thanks in advance for any guidance you can offer!

I generally have to set my thermostats one or two degrees higher than the temp on the glass. 91-92 depending on the enclosure to achieve 89-90. Glass temperature is more important than substate temp as my snakes move substrate to the side and eventually are just sitting on glass.

90 degrees surface temp on the glass is fine, and actually ideal.

You can mist as often as you need, as long as the enclosure is not wet for long periods of time, which can lead to scale rot and bacterial growth.

Keep in mind that you will have to find a way to bump up the humidity to around 70% during shed. I would make sure that's possible before you get the BP.