Your temps are gonna flucuate but they should be sitting in the 88 to 90 range and thats perfect. Keep in mind the fan should be runnin 24/7. The fans purpose is only to move air not to cool. Therefore you dont need a big fan. Just something to move air. In my walk in incubator which is 5 ft wide by 4 ft deep by 7 ft tall only has a small computer fan running. It keeps air moving without cooling. I also have 6 buckets filled with water with tops to help hold heat. Now scale that down for a smaller bator. I have one egg box with the same mix in it just for my probe. This probe box sits on the middle shelf. Sure there is a little flucuation between shelves but as long as your steady temps are in the right range your good. Keep in mind for thousands of years in the wild these snakes have been incubating eggs and the temps are never 100% stable.