@Bluto

Nice post. I think you're on to something. I would only add that there's some non-zero overlap between some of the groups. NI & V, and P & V, at least. If we knew those numbers it would make things 'fit' a little better.

Diamond Princess being pre-Delta could also make NI=0.8 an unreliable assumption.

If we had solid R and case number data, there may be a way to back into a good guess for SUS based on population density in hotspots. That's just a hunch, though.