Parked on a slope with car still hitched...

I would never dream of just using my x-chocks without the wedge chocks. I haven’t had a problem with either because of cooling tires. Without a doubt, tires will shrink as they cool. But, as they cool, the pressure also decreases, with the bottom of the tire flattening. As this happens, there will be an increase in diameter of the tire.
Now, how much those measurements are, I have no idea. Maybe one compensates for the other. My guess is that both are very small. As I said, I have not noticed a problem and I have checked. I do not doubt SoundGuy’ s account, I just have had a different experience.