Yes, I see. It would be a vision center if the head position that made the 1/2 ball cuts appear the same cutting left or right made a stop shot look dead straight.I'm not exactly clear on all of that. My recollection is that I wanted to find a head position where 1/2 ball cuts appeared the same cutting left or right. That position is not a vision center as defined.
Having said that, sometimes on cuts I invite a student to move their head laterally off VC, to better see the target on the OB/overlap/ball path to center pocket. However, that exception is typically for rather thin cuts. So if we were working together:
1) We would test VC on fairly thick angles, not half ball hits
2) We would discuss your aim perceptions, how you try to aim a half ball shot
3) Etc.