The only other thing I would add to this thread is the small flame could be caused by rust partials falling down inside the burner tube blocking the propane flow. I used to get rust flakes that would fall down from the flue that would block the slots on the burner tube that I would have to vacuum off or blow off with a straw. After a while this would no longer work I removed the tube itself to clean it and the orifice and noticed the tube was filled with very fine rust like a power. I cleaned that out and all was well again. The slots in your burner tube look good after 17 years so your air mixture is probably alright. If you haven't cleaned the tube out recently try that first and see if that helps.