you are right. all the times i have P-1'd at the airport was when on a FC/BF reward with a Y seat assignment for a particular segment. I figured it would be the same for FC upgrade rewards, but i guess not.

regardless the OP will be first in line for EUA should any go through prior to airport control of the flight.

to whiteknuckles...
regardless of the rules, id still make my case at the airport if you have not been up'd prior to arriving. the agent will be able to see that you used miles and were only up'd on one segment and may be more apt to force your airport upgrade as opposed to letting the system do it. but the rules are indeed the rules.