It looks like the dorsal turret (at least) is at 90 degrees to the rest of the ship - you can see that ladder that accesses the turret behind the gunners seat, with the ladder on “floor” relative to the person in the seat.
Like I said, probably the gravity field for the turrets is fixed to the “bottom” of the turret, on both guns. Even on the ventral turret, you’d want the ability to track the gun “up” through the full 180 degree arc, without falling out of your chair at the end because now you’re upside down.