VPI JMW 10.5 damping oil question

I have another VPI JMW 10.5 setup question. I was experimenting with adding damping oil. According to the setup manual, I should fill the oil cup ¾ full such that it will not overflow when the arm tube is set in place. The underside of the arm there is a half-sphere object with a deep conic indentation in the middle. When the arm tube is set in place, the indentation sits on the pivot bearing so I assume the surface of the half-sphere should be immerse in the oil cup. What puzzles me is that no matter how much oil I add, even up to the rim of the oil cup, no part of the arm tube ever touches the oil. Is this normal? If so, how does oil damping work if nothing touchs it.