They do have a fascinating business model.
I'm guessing they categorize the carrier interface charge revenue as ancillary revenue. If so, at $16/segment that gives them a nice headstart toward $82/pax in ancillary revenue. I don't see a lot of people paying for carryon bags on Frontier but they do seem to do a brisk checked luggage business at the ticket counter which definitely helps. Add in some seat assignment revenue and miscellaneous services revenue and I can see how they get to that number. It would be much more difficult to hit without the head start from the CIC.