I had lower 1/3 fog in my headlights on day one. It never went away even after long drives. I told the dealer and they put in new headlights - they were foggy by the time I got home and wouldn't clear on their own.
I removed the sealing cap, turned the lights on to help warm them up - and took a heat gun to gently run all the moisture out (took about 10 minutes each on low), put the sealing cap back on and now they're clear. I think part of the problem is they're sealing in whatever the ambient atmospheric humidity is and it's got nowhere to go.
I have a headlight rock chip (clear bra) kit - haven't put it on yet - but wonder if that would give it an "insulation" factor that might help - these are the thinnest headlights (plastic surface) I've ever seen.
???