To ride on KMG's coat tails, I would not be comfortable with a temperature reading over 95 at any level of substrate my BP could reach. Like KMG said, substrate gets moved around an inevitably you'll end up with a BP lying directly on the bottom of the enclosure without any substrate below them. You still want this place to be at a safe temperature for them. 100+ (even 97) is definitely not a safe temperature for your BP.