How does ELRS failsafe occur!

Hi everyone.

Here’s a query about failsafes.
I’ve got LQ and Rssi dbm in my osd. LQ rarely drops below 90 and rssi dbm drops in predicable fashion the further out I go.
I’ve got the Betaflight OSD alarm set at -109 (6 above the max of -115 when running at 50hz)

My Radiomaster Boxer has a settable alarm for LQ, might it have an rssi dbm alarm too?

BUT - at what point does the rx (or is it the FC) decide that enough is enough and go in failsafe?

Is it a dbm value, LQ value? Can I change it?

Or is a more complicated packet situation?