Had a chat with a colleague who works "upstairs". The ULV is not due to an "excess" of aircrew, it's due to CX's usual incompetence that has resulted in a misallocation of aircrew on the wrong fleets. The true measure of aircrew levels is whether or not all allowed leave is allocated across the airline. In fact, they barely allocated little more than half this years leave (doubt that, go and have a look at available slots vs number of crew in each position and base).