I experimented a bit more today: it seems to start disconnecting/connecting the PV array when the float voltage is set to a value lower than 57.1 VDC. I'm guessing that it can't bring the voltage from the array close enough to the normal float voltage, so it just drops the array (in simplistic terms).
I originally based the wiring of the panels on wanting reduced current and the Must Power clone unit, which indicated that up to 130 VDC was acceptable (the panels don't seem to get above 121 VDC open circuit) - whoops. I'm really not in the mood to rewire them haha 😂.
Thanks for the insights/verification of my unit's config^