I'm not sure that QF allocate "X" seats to a particular airline. I think that the "X" seats go to whoever calls first for the seats, regardless of whether the caller is calling CO or any of the airlines QF has a agreement with, and there are many. I have heard, and would not be surprised if true, that X=2.
There are only 14 FC seats on the 747s that got LAX-OZ and I suspect that they would like to sell a few