Originally Posted by Fast6

3 ways to know:
1) written policy somewhere (not aware of this, but perhaps it's in fine print somewhere)
2) access to loads, upgrade requests, and granted upgrades on a given flight to reverse engineer it (fat chance of this happening)
3) anecdotal evidence of someone chiming in with "I lodged 2x RU for Y-BP and got put in PE with 1x RU back in my account"