TL;DR: Problem solved. Turns out (in shock+contact mode anyway) the panel registers the shock events from this sensor as “open” and “close” events in rapid succession; there is no distinct “shock” event (which is what I was watching for). So it was probably working all along and I just didn’t realize it.
Looking at #13 in this thread got me thinking about this possibility, and perhaps it’s where Tyler G was trying to lead me.
I did as Tyler said, taping the magnet to the sensor to ensure the contact stayed closed and then did some shock tests, which registered as “open” followed immediately by “close” events on the panel, all while the reed switch contact definitely stayed closed.
So it came down to a bad assumption on my part. Thanks much for the help Surety Team, much appreciated 
!