Right on the glass, under the substrate. That was I know the hottest possible spot by bp has access to is 91 degrees, and just above that is a degree or two less. Mind you, I don't use substrate anymore - I use Scott Shop Towels.
Jeez, I can't spell.
1.0 Normal Ball Python- Little Dude 0.0.1 Albino Kingsnake - Weiner Missi