I explained it as simply as I could. And that teacher was an idiot. You have the discussion at the level of the student, but the goal is to get the student to learn, increase his vocabulary and to learn on his own.
Let me dumb it down some more for you. Do not make the port smaller than the head, ever. The goal is to make the port in the manifold the same size as the port in the head. If there is a mismatch, make the manifold bigger than the head, just enough to get everything else lined up.
Was that simple enough for you?