I just helped book this for a friend's return home from their honeymoon. They booked HKG>LAX>CLT>CUN one-way for ~$1153 a person in early Sept 19. It will be their first (technically second since we're looking to use points to book them in biz on their way to their honeymoon) experience in biz so I'm excited we were able to get this booked at this price.
I'll second @
stephem's comment that the availability really does vary based on POS. We were struggling to book through the .hk website and happened to switch the POS to US on ITAMatrix which showed much greater availability and allowed them to get their preferred date.
Using the routing code "F ..I-" along with Departing From: HKG and Destination: CUN (or SJD) allowed us to see which routings would pull up at the lower price. I toggled the sales city back and forth between HKG and US in order to see which dates were available in each POS. Thanks again for everyone who included their tips in this thread as it was very helpful throughout the process!