I went to the bike show a couple of years ago with a friend that was a new rider and needed a new helmet. He had been trying on everything he could find, and they all hurt. He has a more oblong shaped head. At the show, he started telling the Arai guys his dilemma, and they spent about an hour with him taking measurements, trying helmets on, and so on. They said they thought they could fit him, but not with anything at the show. They sent him a helmet after the show, and it fit him perfectly. These guys probably made a customer for life with this effort, and an ambassador for Arai.
That said, Shoei fits me the best after trying on everything for years and years. Guess what I wear......