My six week old son has one ear that appears larger and thicker/puffier in the lobe and outside edge than the other. It is not hot to the touch or redder than the other ear. It is his right ear, which he tends to lay on more often. I just noticed this a few days ago. He is just getting over a fairly mild upper respiratory infection.
Yes, this can be a normal variation, and it could be related to his sleeping posture. Don't worry, unless it remains the same beyond his first six months. Once he starts to sit up, the asymmetry is most likely to disappear.