I requested BEX (Business Extra) upgrades for my wife and I on a long haul. Because of this, they had to split our PNRs (but said they would keep us linked at my PPRO level). A few weeks in advance, mine cleared and hers did not. As day of flight neared, J sold out and remained 0 until flight time. The first problem I saw on check in was that her BP showed group 3, though if she were linked to me as PPRO she should have been group 2. So maybe she wasn't properly linked for upgrade priority.
We went to the AAdmirals club and I asked the agents to make sure she was prioritized with my status and with the correct priority code for the upgrade instrument. The woman was helpful in looking into this and showed me the screen that my wife was flagged as BEX, and below the pecking order of VIP and MLG upgrades within same elite level. She also confirmed that BEX upgrades fall below the other instruments (other the the complimentary upgrades, when they're in the mix). So it's VIP#->MLG#->BEX#. This seems to mean to me that one the flight turns over the airport the BEX instruments hold lower priority (all other things being equal) than MLG and SWUs.
That is interesting, I had previously thought that "C" inventory upgrades -- whether SWU/ VIP or Mileage, or Business Extraa were classified first by corresponding status group, and then ordered by time of request. Did the AAgent also explain where "R" upgrades were on the gate upgrade list?
In any case as a best AA frequent flyer practice, BXP upgrades should be redeemed before departure, and preferably before the e500-sticker upgrade windows open at T-100 hours (four days before departure). This is the great advantage in fact of these BXP or mileage upgrades, that they are confirmable when C becomes available, possibly long in advance.