First its very basic. Reptiles do not have a set temperature to exsist.(like a mammal) They use a range of temps. Please keep this in mind.
What your seeing are telltail signs. When a reptile grows short and thick, it simply means it cannot get to the prefered temps. All colubrids and most reptiles normally grow long and thin.(for the species) Then bulk out when they reach sexual maturity.
Please consider, because your snakes are feeding a growing, they are close. So your temps are not that far off. Remember, the difference between nature and captivity is basically a lack of options. In other words, we restrict their choices.
Todays average cage is very, middle of the road. That is, they are small and offer only medium temps. They are normally to small to achieve a wider range.(rack systems etc.) Reptiles normally pick extremes for specific purposes. Heat for expending energy, like digesting food, growing, shedding, and some stages when gravid. And of course to heal injuries. They choose cool to conserve energy and conserve moisture. Again simply put, obtain energy and conserve it for specific purposes. I hope you understand. I have found most kingsnakes use a range of, 45-65F cool end, 85-100F hot end. Those are year around. Thanks FR