When trying to remove the oil filter bolt with a box-head wrench, I could felt the head starting to distort. But when I used an hexagonal socket, it worked well.
Box-head are suppoused to be better as the apply the force on the sides of the nut, not the corners. But for the oil bolt, a fit socket -hexagonal-is the best option. And the same goes for the valve inspection caps. A box socket, and a slight-but-firm blow of the handle -like if it was an impact wrench- works well. Common sense to start from light blows and gradually increase the force to feel whether the head is being damaged or not.