Achieving proper temperature gradient thru several inches of substrate? (TL;DR)

[BonnieBallPython]

88 is fine. 90-91 is okay but is also right at the border of too hot. Shooting for 88-89 gives you a small buffer in case something goes wrong so your snake avoids injury.

The main concern I think we have is there's something that is making your BP avoid the hide and it could be the surface temps are actually above that 91. The heat gun when used correctly will give you a much more accurate surface temp. Using a separate thermometer may have the temps off slightly because of the housing on it, if the snake moves it away from where it needs to be or if it pees on it.

GoingPostal also has the same concern I do, if you are using a thicker substrate, the bottom of that terrarium will be HOT. Make sure there's enough airflow between the bottom of the tank and whatever it's situated on to avoid damage. I saw one used wrong once (didn't put the sticky feet to raise the tank) and the glass bottom just shattered.
Also using our own senses for a feeling of heat can be off. for example, our natural body temp around 98 is actually uncomfortable for a lot of bps when directly contacting us. So what seems warm to our touch may be too much for them when you feel the substrate. You do need to be accurate and that heat gun is the way to go with the thermometers being a casual check in. You still want to check them regularly with the gun as well even after properly adjusting

If your night temps are never under 72, I would not even bother with a second pad. Your snake will figure it out and head to the warm hide as long as it is the proper temps.

There are indeed sticky feet on the bottom of my terrarium!

She seems to have no problem roaming around the warm side of the tank, she just doesn't sleep there. I've seen her rest her head under the lamp a few times, though she's usually not awake when it's on anyway.

I'm wondering if she just likes the shape of the hide on the cool side. She sometimes picks a different hang-out spot after I've cleaned and re-arranged the tank. I might try swapping it around later and see how she responds.

I'll take everyone's advice and buy a heat gun. In the meantime, I will continue keeping an eye on my thermometers.

Guess I don't need to go any warmer. Thanks everyone!

[Armiyana]

I'm wondering if she just likes the shape of the hide on the cool side. She sometimes picks a different hang-out spot after I've cleaned and re-arranged the tank. I might try swapping it around later and see how she responds.

This could also be the case! if they are different that might be why she's avoiding it. They can be really picky at times. Maybe the warm hide doesn't feel as secure. They tend to like tight fits that are well hidden more than open spaces.
If the temps are correct after all, then I would try to figure out why she isn't comfortable there. On some of my fastest growers I switch hides out so much cause they just start outgrowing them so fast but anything too large and they get fussy. lol

I'm glad you put the little feet on! a lot of reptile branded terrariums now come with little open plastic rims on the bottom so you don't always have to, but better to be safe then sorry. Especially if it's just a regular flat base one.
When you get the heat gun, I would make sure to temp the glass as well as the top of the substrate. Just in case she ever tries to burrow down to the bottom (it happens alot with my girls) you don't want it being too hot there as well.