in africa the day time temps spike over 100 and dip at night into the low 80s to high 70s most of the year. therefore these animals are used to a temp flucuation. yes the ideal body temp is 89 degrees. if you have any doubt your hot side isnt hot enough you can bump the pad up. with a substrate over the pad side you can go pretty much as high as that pad will go. if your snake feels its too hot he will go to the cool side. if you see him hangin out on the cool side alot then drop the temp a few degrees till you see him hangin on the hot side a little more. sometimes you can overthink with all the different caresheets out there. i have always kept all my thermostats on all of my racks at 89 degrees to 90 degrees and night drop 10 degrees during the cooling season for breeding. about the only time you dont want the temps to flucuate more then a couple degrees is during incubation. remeber that ball pythons are a species of snakes that can regulate their body temps. they do this when they maturnally incubate.