Keep in mind because of the relatively overall short length of the 3-18 and lengths of the scope in front of and behind the turret housing that the angled portion of the objective housing can sometimes interfere with the front of the scope rail on a short action if the rings are too low.
Look at the picture in post #6, if those rings were lower the objective housing would probably hit the front of the scope rail.
On a long action where the rail extends further forward it's going to be a real concern, and might require taller rings to keep the objective clear of the scope rail... which might make getting a solid cheek rest difficult as your PH stock doesn't have an adjustable cheek rest.