There are a lot of factors that can affect the available seats in F, and it's always surprised me how fast that can change shortly before a flight. At the end of July, when they were still doing DM upgrades on the transcons, 20 min before boarding a JFK-LAX flight, there were 7 seats, 10 min before boarding, there were then 2 seats. As Mrs. TrojanTraveler and I were #3 and #4, we then started to call to get a regional cert applied. As we began the talk, 5 min later (so 5 min prior to boarding) there were then 5 seats available. (So we didn't apply the cert.)

To me that's a fairly dynamic up and down in available seats, especially given that it was immediately before boarding.