I would guess that wild cornsnakes most often face directly into the sun [when basking].
Here's what I am thinking...
(WARNING: I am about to ramble.)
The idea of the cornsnake's wavy basking position being a method of disguising its shape from potential airborn predators never really sat right with me. In my opinion, the wavy shape is the quintessential snake shape. This would not be too effective of a disguise.
Then I thought about snake behavior. There are only four things that a wild cornsnake would be concerned about -- shelter, food, predators, and heat source (sunlight). This behavior would have little to do with shelter. I doubt that the body posture has anything to do with luring prey items, and I do not believe that it is an effective disguise either. That leaves me with the heat source option.
I would think that reptiles would be EXTREMELY conscious about the heat source (sunlight). In fact, several species will manipulate their bodies in order to increase the natural heating effects. One example that I am personally familiar with is the Russian Tortoise. This animal will often prop itself up against a rock in order to angle its carapace (top of shell) directly toward the sun. (This is sometimes referred to as "tilting".) This allows for a more uniform heating over the carapace area.
I wonder if a similar technique is employed by wild cornsnakes. By positioning itself directly into the sun's rays, the cornsnake is optimizing the coverage of sunlight over its entire back. (In other words, if the snake was facing sideways, then half of its back would be in shadow.) The sides may still catch a little sunlight in a straight body position, but by utilizing a wavy body position, the various points along the sides are now fully exposed to the direct sunlight as well. This would seem to be the ideal position for optimizing the sun's warming rays. The back is fully exposed to direct sunlight as well as many points along the sides. (And it would also be expected that the cornsnake would periodically readjust its winding body position so that the temporarily unexposed portions of the sides are now fully exposed to direct sunlight.)
This would be the most economical way for the cornsnake to optimize the natural heat source. And since other reptile species (Russian Tortoise, etc) express similar sun-catching behaviors, it would not be ludicrous to expect a cornsnake to do the same.
Who knows?
Chris