Ok now I am confused. You have 82/90 currently? What is the problem? Are you trying to drop the max temp of the flexwatt?

I too have read tech info from Calorique that stated not to run their product over 110 for extended periods. I have not tried to use back heat my snake room is quite cool and I have needed to insulate the rack and run 4 inch and 17 inch to hold proper temps.

I suspect that if you wish to drop the flexwatt temp you will need to use belly heat. I have my temp set to 94 and get 91-89 in the rack (different levels) I would suggest that a fail safe is the best option to insure the safety of your collection. You might also look to different wattage flexwatt to further increase safety margin the lower wattage's for a given size have a lower max temp. My rack unregulated produces 100/87 this is scary high temps but is tolerable for the snakes for a short period of time.