I have very limited experience, indeed, but (as a lowly Oneworld Ruby) over Christmas I flew with my partner (different bookings, as different return dates) MEL to HKG (no offer) and HKG to PEK (offered upgrade for me, but I declined rather than asked for her to be op-uped to join me, perhaps a wrong question from me in retrospect). On the way home, no offer from PEK to HKG, but op-uped from HKG to ADL.

From this very limited sample, I was offered an op-up ex-HKG both times (as a lowly Oneworld Ruby) but not from other ports. Perhaps they are more generous in HKG? (Loads didn't really seem to explain it from PEK at least.)

On an unrelated note, I'll be flying CX again - my usual airline is QF and op-ups there have been exceptionally rare for me, but I had 2 or 4 offers of Christmas on CX. That would absolutely make me switch airlines of preference! (And I like the CX service too.)