Isn't the official capacity 21.5? Then the next question is- is it possible to actually fill the tank completely?
Years ago I had a Taurus SHO and I never put gas in it within 5 gallons of the stated capacity. People thought that it just had a big reserve when the gauge said empty. So I didn't worry too much about finding gas when it got close to E, then one day it ran out. I walked 4 few blocks to a station and borrowed a can. Then I drove back to the station and filled it up. When it clicked off 4 gallons shy of the stated capacity I kept slowly trickling gas into it until I got the full stated amount in there. So 21.5 gal. capacity is great but not if you can't actually get it all in there.
I don't think I've ever put more than 17 gallons in my JLU Sport.