So, Finn's ability is in arc. You have Finn, on a Ghost (VCX-100) w/the Phantom docked. Since the special firing arc is still a "arc," you get to add Finn's die when shooting from the rear right?

I presume the same would work for Finn on the ARC-170 or Auzituck.

Correct.

But not with something like the Falcon, since a 360 arc means you can shoot outside of your firing arc, so it's not a firing arc.

THe Falcon has a primary firing arc.

It can also shoot outside of it with its primary weapon.

56 minutes ago, Celestial Lizards said:

But not with something like the Falcon, since a 360 arc means you can shoot outside of your firing arc, so it's not a firing arc.

No one has a 360-degree firing arc.