This has been raised several times in the past already, and not only with respect to the CN zone. In response to such requests (among other things), the monitoring system has been enhanced so that it is easier for people with a track record of hosting a server to also host monitors. And it worked, there are now well over 150 monitors for IPv4 from all over the place.
However, for some reason, out of those well over 150 monitors, there is only a single one in the CN zone. I’ve wondered before why that is.
So you guys in the CN zone need to figure out amongst yourselves why there are not more monitors in the CN zone. Setting one up is easy. The prerequisite for hosting a monitor (having had a server verified for at least 18 months) can be waived for cases where this makes sense, and where the pool would benefit from more monitors to increase diversity (send an e-mail to server-owner-help@ntppool.org).
For the same reason that you rightly write that a bad score from a monitor far away is not necessarily indicative of how the server performs for more local clients does it not matter when a monitor is giving bad scores to servers far away. Even any issues in between ISPs within the CN zone should not be a deterrent not to run a monitor within the CN zone. I assume even regional ISPs within the CN zone have enough customers in them to be worthwhile to be represented by a monitor within that ISP network. Only the uplink from the monitor needs to be stable, not so much the inner workings of the network farther away, as the latter is precisely what a monitor is supposed to assess.
One challenge is that the monitoring system itself is biased in the sense that the health of the monitors themselves is evaluated against a fixed set of reference servers. And those are currently located so as to disfavor monitors in many places in the world. E.g., there is a single monitor in India (another place that would benefit from additional monitors), and it is not monitoring most of the time because it is sanity-checked against reference servers “far away”, and due to that is considered having a bad clock most of the time when it would be ok with respect to more local references. That bias is another problem, but again it should not be a reason not to run a monitor. Only when we learn about such issues, and they are exposed, can there be improvement in those areas, at least potentially.
So please communicate within the local communities that the pool not only needs more servers in the CN zone, but more monitors as well. Reach out to universities and companies, and invite them to host monitors for the pool (and servers).
And, if you have a stable uplink, host a monitor yourself.