Yeah a 180 arc totally works on a small base, but looking at the toy SF TIE/fo I'm pretty sure it rotates 360.
It may be able to rotate 360 degrees, but because of the wing panels, it can't fire into it's left and right 90 degrees.
Given that they're just a couple laser cannons. It makes sense to use the ships primary weaponry to fire forward, and just leave the swivel guns to fire backwards, since you can't fire two weapons at once in this game(if this were more of a simulation, then you could totally fire both forward at the same time for increased firepower. But currently, the Titled Y-Wing is the only ship in the game that can do that).