Ok as an agent I will tell you the gospel truth about econ plus. Most of what has been said here is mostly true.
1) Econplus is reserved for Premier and higher travellers or full Y, B or M fares. Those are full fare coach and Silver and higher. Silver and higher on US and Star alliance as well.
2) on most of UA
's narrowbodies all the exit rows are in econ plus so the exits fall under the same rules.
the flight is wide open the agent has the DISCRESSION to put someone up there provided that ALL
of the folks who are entitled to econplus already have it.
4) The gate agent also has the dissgression to put someone up thier if:
All of the seats are taken on a full flight and thats all thats left. (read middle seat)
They release the preassigned sests at 20 min prior to departure and some seats are available.
5) on light flights the premier sections middle seats are blocked for the comfort of the Premier members and full fare members. Don't be surprised if an agent tells you thier are no econplus left and there are middles still open. Thats the way its supposed to be.
6) ASking doesn't hurt. But if your told econ plus is unavailable you now know why so don't gripe at the agent. It will NOT make an econplus seat come open for you.
7) the major thing agents DO
NOT want to happen is a Global services or 1K sitting in the back, when they moved Priceline passengers to econplus. So if you buy priceline or cheap tickets, understand that the agents are just trying to protect those seats for serious bigtime travellers.
A little less Hooah, and a little more Dooah.