One of my two cats is losing hair on the back of his ears BUT it does not seem to be caused by mites. First, the veterinarian says mites typically cause hair loss on the tips of the ears but in this case the tips are fine - it is the backs of the ears only that are affected. Second, the cat is NOT scratching the ears at all. I live in a small apartment, generally work from home, and this is a lap cat.

I would have noticed unusual behavior and I haven't seen him scratch even once or bathe the area excessively. In fact he exhibits no other strange symptoms at all and seems to be oblivious to the problem. And finally, I have treated for mites with a strong medication I received from the vet and the hair loss has only spread since then.

The vet seemed stumped and I can find nothing online that does not automatically link hair loss on the ears to mites. So if anyone has any experience with a similar but DIFFERENT malady I would very much appreciate hearing from you!
UPDATE: My vet did a skin scraping and looked under the microscope, so we've confirmed that there's nothing alive causing the issue. No mites.
It's possible your cat is having an allergic reaction to his food. Grains like corn can be allergens. Try switching to a grain-free wet food for a few months. At this point, what do you have to lose by trying this?