By controlling the number of vacancies management does control where new hires go. On the -400, ANC has 200 F/Os for 72 Captains. CVG has 87 F/Os for 84 Captains. And JFK has 37 F/Os for 56 Captains. So at least 19 F/Os get pulled out of their base (which can be a good thing to avoid taxes) to be paired with JFK Captains.