I'm thinking it might not matter at all - I checked .bom for upgrade using miles OAK-ORD-BTV - showed all F seats open, called UA to make res (I'm 1K) and was told no UG seats available on my flights. She looked with me - no seats in first were taken - but neither were they available. 319's, CRJ's, 757's via ORD and NO AVAILABILITY? Nope, no availability. Called back and used the Regionals, got upgraded all 4 legs.