Around 100 is fine in some areas towards the bottom, higher than that is unknown. I keep mine at about 90-105 towards the bottom, they mostly bunker down towards the bottom. The egg flats are their cool off area. My whole ground floor is covered with a heat mat so they can't cool off down there. If they're mostly on the bottom then that means the temps are fine down there. Keep them that way, they will choose where to go. I know ideally you should just have it 90-95 throughout for optimal breeding, so just try to achieve that and you'll be good.