[C210N]

100 to 200 feet at night? barely less than a wingspan?

dicey enough during the day.

well, it’s a theory!

[zipper]

C-5's (and C-17's, etc) do it at night too. The strobes are a nuisance, but further away it's easier. And the host is holding a steady speed and altitude.

With the transponder off they can flash their weather radar within 25 miles or so to get a skin-paint range estimate.

And a portable ADS-B receiver might prove useful for that purpose, and for ID of who they're joining up with. The call sign will be their clue to the destination.