Actually if you look at the average highs and lows for Ghana Africa you see that it very rarely gets up to 90 degrees for an average (though the hottest part of the day can hit 100, snakes are usually underground at that time) . I actually shoot for the high 80's as a hot spot and the lows are whatever the ambiet temperature in the room is (my herp room typically is in the mid to high 70's but can go as low as the high 60's in the late spring or early fall) I've always thought that 92 degrees for a hot spot was too hot.
I think the temperatures that you're talking about were derived from the high and low temperatures inside of a termite mound (which is a favorite denning spot for these snakes)