My guess is that it is all about yield, not capacity. Just before Easter I flew in PEY on CX254 from LHR to HKG. I booked my ticket around six months before. I was checking the fares again four weeks prior departure. There was only Y-full fare available for sale, PEY wasn't even bookable. The same situation a week before departure. I was expecting a very full flight out of London. However, when I checked about capacity at the lounge I was told that the load was very light. Indeed, there were not even 100 passengers waiting at the gate and PEY was almost empty. It looks like CX is optimizing its yield....