It was quite strange actually - as my roster with Astraeus was as a 'Pollyfilla' (fill the gaps) I quite often found myself 'off' flying for periods of a few weeks. After one of these occasions the F/O (PF) called 'F30' from F15. It seemed to be safe, so I did it, and on the turn-round asked why. Apparently one of the new 'wunderkinds' had introduced it as 'the way to do it', so it kind of stuck. I had a personal 'NTO' on it, so no big issue. I continued myself with a F25 selection since there was nothing in the manual to say otherwise. Who cares really? There were bigger things to worry about.
A while back I retold the story of my trip as a new F/O with a 'previous' to Funchal when on one occasion the Captain briefed and 'did' a call for F40 from clean downwind. It worked perfectly.