If only the person in 1F knew the difference between 1A and 1F.....he/she wouldn't have selected 1F . I've been sort of lucky, as I've flown this a/c to/from Hawaii a lot. There's a lot of travelers who don't fly UA or this a/c or in First Class a lot and I see they've taken 1EF and leave 1AB open . Kareem Abdul-Jabbar could probably stretch out in 1AB and would have his knees in front of his chin in 1EF.

Edt: I just looked at SeatGuru and description for 1ABEF are the same, commenting that they all have limited room because of the bulkhead w/ no mention of AB cutout. This may explain why AB are open sometimes when rows further back are filling. I'm not inclined to correct them ..