Suggest making the turrets more orblike in order for whatever base material it sits on does not interrupt the bullet trajectory.
I'm sure you could also just fake the POV.
In any case, it would seem that two stems that are sticking out past a wall should not ever point directly down towards said wall and be able to shoot it while you are inside the turret.
TLDR; I would like to be able to shoot down at invaders while in a turret.