Up to a point, you do not want the plug to protrude up so high it gets in the way of things. A strong enough magnet exerts its field out into the oil without having to stick up further, gets the job done without being in the way. One of the most common ways to pick up metal in the oil is to surround the filter with a very strong magnet, so nothing is actually protruding into the oil, but rather the oil flows over a magnetized surface, but this gets expensive:
