I know this is a pretty elementary question, but I have tried searching around on here and in a couple of the usual places, and I'm finding surprisingly little description of just how/what the Squelch Fine Tune setting for APX radios (perhaps for this setting in general) actually corresponds to.

By default the codeplug in my unit came set at 3, but this seems rather loose as a default -- I've noticed the radio falsing open on rebanded VHF channels that are near-adjacent to a booming MDT taxi operation, for example. If anyone can provide some empirical data on their squelch settings (what and why) for the APX portable series I would be very appreciative.