So what happens when the circling MDA for your category is governed by an obstacle at the extremity of the protection area, or even on the opposite side of the aerodrome, if there's no circling restrictions? I don't know how Pans Ops is interpreted in other parts of the world but, here, I can descend - provided that I have visual reference - to an altitude that gives me the standard obstacle clearance height for my category.
It certainly helps if you know the aerodrome and the obstacles in the vicinity. However, if you're visual and have good visual reference from the cockpit (obviously some aircraft aren't as good as others in that regard), and can identify a height of 300, 400, 500 etc feet above an obstacle, you can often descend a bit sooner in complete safety, if necessary.
Of course, as I said at the outset, it's a matter of how Pans Ops is interpreted in your part of the world.