If your hot spot is correct then you've got good temperatures. It may not be in your ambient room temperature but if there is enough of a hot spot then somewhere in their enclosure is the temperatures they want. The heat radiates to slowly go down to the lower ambient temperatures from the hot spot. It doesn't just go from hot to cold from one spot to the next so the snakes do have a variance in temperatures within the enclosure to find their optimal spot. I would recommend trying to raise the ambient temps but I wouldn't say that its a dire concern for the snakes health.