!!! Wow. NOW I UNDERSTAND! CX has limited visibility into their F loading because of partner cancellations. This explains the seemingly bizarre phenomenon below, which I've encountered multiple times (including this month):

1.) Try to upgrade J to F about a few months in advance. I am MPC DM.
2.) Told award inventory sold out.
3.) I waitlist. I don't clear, or take myself off eventually.
4.) I GET AN OP-UP TO F.

Yes, on multiple occasions I have gotten op-upped to F when I tried 1-2 months prior using my Asia Miles to upgrade to that very F seat I ended up getting for free. Brilliant.

Before, this situation made zero sense. But I now I get it. CX must have crap visibility into their F loading due to generous partner award cancellation policies! As a result, they aren't optimizing the F cabin yields. CX has no idea what the F loading is actually going to be like because they face all these partner redemption cancellations last minute! So what often happens is, guys like me who try to use our AM miles to book seats fail. So we are "stuck" in J class, until say 2 AA redeemers cancel their F ticket 3 days out. CX can't sell the seat, Y or J is overbooked anyway, and I get an op-up.

Or, even worse (from CX's profitability point of view), ID passengers fill up Y and J class, and then I get the op-up. Either way, it's both crap revenue management and a dis-incentive to join MPC/AM because you're at a disadvantage within your own program!

Obviously I can't be 100% sure, but given the # of AAdvantage members I meet on board CX F cabins to/from North America, I know it's a safe bet to say at least 2, if not more seats on every F flight I take to JFK, SFO and LAX are partner redemptions, not cash or MPC tickets. It would only make sense for folks to behave in the way jamie describes, it's completely logical. I would do exactly the same if I lived in the US and booked to AA. I'm just amazed CX has allowed it for this long. They're leaving revenues on the table.