Has it been determined that the weapon batteries mounted along the edge "trench" of a Star Destroyer can fire directly "upward" or "downward"? If the firing point of the trench weapons is recessed, even a little bit, then the firing angle would likely be restricted such that rotating so the top of the Star Destroyer to face the target won't necessarily allow the side guns of both sides to fire on the target. It seems reasonable that the weapon turrets located along the top of the body near the superstructure could fire directly "upwards", but then, as indicated above, the side weapon batteries would likely no longer be able to target the enemy, so it could result in less firepower overall. This tactic wasn't performed to my recollection in any movie space battle sequences which could be further evidence that this tactic doesn't work.