Is there a a rule-of-thumb for the likelihood of trans-Pacific award seats in F becoming available as the travel date approaches? I usually snag seats well in advance, but this time around I had to cancel my original plans and am hoping to still travel in December. My concern is the trans-Pacific flights.
I’m on the waiting list for two flights. They’re about 3 weeks out, and ITN (seat maps and availability) seems to show 10 and 8 (of 14) seats available, respectively. The other classes appear to be lightly booked as well, so the need for operational upgrades looks to be slim. My questions:

• Is there a rule-of-thumb that correlates the opening-up of award seats to the number of available seats and the number of days/weeks before a flight?
• Are UA’s telephone people generally willing to let you know your place on the waitlist? I have no status now with UA, but have been (earned, not comped) PrEx on multiple occasions in the past.

Thanks for any help.