I would use the full name if I liked it & just tell people that the name is NOT the shortened name. For years I hated people calling me Fi. To me it sounded like a poodle name "FiFi". But I can't escape it & have given up telling people not to call me that. Its weird, as a kid not many people did it but as an adult every other person (especially online) calls me Fi. I much prefer Efjay or FJ (which started here as my username use to be FionaJill) But yeah, I've accepted that Fi isn't all bad & just go with it now.