Yes, I think 22* C. is too cold, but if your snake doesn't want the heat, that's the only choice there is, so if that were my snake, I'd find a way to raise the cool
side a bit (maybe raise the light wattage or use CHE)...26* is more like it. Your snake's choice of the cool side may also have to do with feeling secure (hides).
That's a very attractive set-up, by the way.