I understand completely, but the mind uses all visual data, in addition to any specific reference you might be focusing on.
In other words, when you look at the contact point and estimate how far away from that point to aim so that the cb contacts that point, you're giving your brain the entire visual of the ob. You might be focusing on that estimated contact point from behind the cb, but your brain is getting more than just that single reference. And it's paving the neural pathways needed to recognize shots, cb-ob relationships.
The more you do it, the more visual input your brain gets. Eventually, you find yourself not really looking at the contact point for most shots, because your mind recognizes the cb-ob relationship needed to pocket the ball. In other words, you recognize where the cb needs to be, in relation to the ob, not the contact point itself. That's the end result, whether you develop aiming skills using fractional aiming, ghostball, or contact points.