He may be doing something else toward bedtime that causes him to go to sleep wherever he is.
Most times cats will follow their routine, and if you go to bed later than usual, he may fall asleep wherever you are at the time of his bedtime, and then he will just stay where he fell asleep, when you go to bed.
Cats like to be warm wherever they are sleeping, so if your room has a fan he may not like that, or if he can't snuggle, for example if you are tossing or turning lately, he may leave the room.
Or maybe he has begun to see something out the window at night and he is keeping a vigil and sleeping near the window to watch whatever has his attention. My cats right now are transfixed by the squirrels and birds, deer and raccoons foraging for nuts and winter food to store. So they spend a lot of time at one part of the house where they can see all the activity occurring outside