Were all Arc-170s always crewed and flown with a tail gunner? If not, a title or modification (or crew?!) may be the best way to show that mechanic. APL only works on Large Ships and a rear arc isn't right, but what about:
Tale Gunner, 3 points
"You may make a 2 attack at enemy ships within range 1-2 of your rear arc."
Edited by BaronFel