Its really great that your taking records, but there is a small problem, ok, a large problem.
Your records are great, but your assigning values is prejudiced. In this case, prejudiced means your assigning predetermined values to the unknown. And that means, your conclusions may not be valid.
Lets take your use of the word "active". You say these kings are active at lower temps then other snakes. But you did not find them being active, you found most undercover coiled up or moving, yet undercover.
So what allows you to say, they are inactive or not active???
Lets make a list of normal active behaviors, then make a list of what could be called inactive.
Active lists, just some easy to understand basics
A. shedding, feeding, foraging, mating, nesting, digesting prey bolus, thermal regulating, climbing, swimming, crawling on the surface, moving in any manner. engaged in group behavior, mate selection, maintaining hydration, etc.
Inactive list,
A. not moving, coiled up for long periods, sleeping, resting.
The problem with the inactive list is, how do you know they are actually inactive. This partains directly to your case. You mentioned that they come from somewhere and move undercover in the evening. You got that hint for KY Phil. Another interpitation of that "could be" they actively moved from a resting a place to somewhere closer to the surface to take advantage of higher temps. This would fall under the active list as, thermal regulating, not resting or sleeping, in the inactive list. As they moved from somewhere to the place you are looking, at a certain time means, they are actively doing something. The question is what??
An example for the inactive list is, sleeping, when snakes sleep, their eyeballs droop, that is, their pupil drops to the bottom of the eye. have you seen this? Of course reptiles with eyelids are much eaiser to tell as they close their eyes. Even this can be confusing, sleeping lizards eyeballs bulge out, hiding lizards eyes are held in.
The point I am making is, there are very defined active behaviors that reptiles do, only we never or rarely see them. Yet, most on the active list are common daily behaviors active animals of all types do. Yet, you and I rarely see them do these common daily, or even seasonal activities.
Take copulation, we all know that snakes commonly copulate over long periods in our spring/summer/fall, depending on species, yet, you do not see it in nature. We do see it commonly in captivity. Does this mean they do not copulate as commonly in nature. Or does it mean, we are not looking where they are commonly active? The problem is, where they are actually active, is not where we are looking, this is a key concept.
The key to understanding some of this information is, you must find ways to gather that information. Not just a snake under a board.
The key is, observation. Not just seeing a snake under a board, but observing what that individual is doing under the board. Taking more data gives a better idea of what is actually occuring
For instance, when snakes need heat, they move to a place that has the heat they need. In your case, you should determine what those reasons are. Did they have prey in their guts, a common reason to move close to the surface. Were any in opaque(in shed) They commonly elevate they BODY TEMPS during this time. Did you notice if the cover was in the sun in the day and heated from the days sun, or in the shade not heated above the rest of the surrounding area. Did you compare the mass temps under the AC to other surrounding areas??
In our field studies there are three very common reasons snakes move near the surface, One is digesting food, two is shedding, three, is incubating eggs/embryos. The fourth is, to strengthen the immune system.
The above three or four activities require the highest temps. Other behaviors do not require the highest temps and in fact can be done at much much lower temps. Or a wide range of temps. Such behaviors as prey capture, can be done in a number of ways, with cooler temps, ambush feeding can be done and is commonly done, but active foraging requires higher temps to allow their bodies to move more efficently. In most cases, individuals ambush feed first, as it requires to loss of energy, then forage feed second, which requires lots more energy. There is less actual gain to the individual if it must forage. Also there is far more exposure to danger when foraging. Yet, they must at times do this to stay alive. In our studies, they try to conserve energy at all costs. So they do as little as possible.
The above is very easy to test in captivity, a captive snake will feed well before it crawls around looking for food, the longer you wait, the more it crawls, then if it cannot find food, it will go down and conserve energy(choose cool temps if allowed)
One actual point to my post is, instead of making conclusions, its time for you to ask better questions. Its time to take better observations and data.
For instance, were the temps you cited, air temps or body temps. The reason I ask is, air temps are not so important or accurate to snakes, mass temps are very important and more accurate. The area under those boards is important, not the air above the boards. More importantly is the Internal body temps of the snakes your finding. Are you taking those, and yes, there are many body temps that can be taken, Cloacal temps, bolus temps, head temps, are important and commonly different, depending on need and activity.
More, when a snake voluntarily moves from a temp to a different temp, is key to understanding its needs, not its temps when if first coils up to gain or loss heat. At what temp does it choose to change its behavior?
As normal I go on to far, but hopefully you will get the point. In your post, you state kingsnakes use lower temps, in order to say that, you would need to fill in the above and compare it to those other species information, taken in the same manner. To make a comparison, they have to be in context to eachother.
Any questions, hahahahahahahahaha Cheers and keep up the observations.
