Bear in mind that the OPUP is only to avoid an oversale, so even if J is overbooked, that does not mean an oversale. All it takes is one J misconnect and the need to OPUP someone goes away.
I also question whether if F is truly empty and there are no nonrevs to fill it, whether UA will OPUP someone before it downgrades someone on an award or GPU to Y (presuming space in Y).