Observations on the carry handle sights:
I had suspicions on what the "rear post" sight was for, and I think this confirms it:
On the Military models, the front sight hood has a pair of phosphorescent dots. The rear post then also has a dot, and you line them up like a reverse pistol sight for night shooting. Because the entire front sight hood is shifted left and right on the originals, you retain your zero.
Another point of interest is that rather than having its own setting, the night sight is on the 300m setting. A lot of Canadian shooters have noted that our 100m aperture is ridiculously small, and instead use the more comfortably-sized 300m aperture.
What if this is intentional?
The USMC zero their rifles for 300yd to minimize or eliminate the need to adjust your sights or use holdovers over varying distances, as described here:
The Russians use a very similar 300 and 400m zero for their 5.45 AK74s and RPK74s respectively.
Chinese 5.8mm ballistics being similar, I'm wondering if the intent is to zero with the very precise 100m aperture, and then use the 300m aperture as a battle sight from 0 out to 400m. Further than that you flip up the 500m sight.
Its super hard to find confirmation of this, as friends with relatives in the PLA "Don't remember" anything about their service weapons, either intentionally, or from disinterest, or perhaps they were not even given that level of instruction.