I don't see any difference in point 1 about perceiving the 2 lines. Yes, there are different line, but 2 are chosen to get the visual... somehow, with a lot of practice... hence, not a very explicit direction.
While the pivot has been said to be at the bridge V, some have said it doesn't at times and every time I've clipped frames from people's videos demonstrating the manual pivot, they have bridge shifted and had a significantly longer effective pivot axis. Hence, observation indicates this is not explicit.
On the tip diameter, check my analysis in the thread analyzing Stan's pivot, where starting 1mm away will lead to about a full pocket variation of OB on medium long shots.
And the air pivot, is much like the visual perception, not an explicit direction, unless instructing one to practice it a lot is explicit.
Cheers,
Colin
Actually, Colin, it is explicit instructions. It's just that you are so focused on other irrelevant material that you totally miss the actual instructions. You say that you have seen and heard different people pivot differently. For starters, forget about the pivot. What you are doing is planting your bridge hand 1/2 tip from center according to the visuals you obtained. Then, you look back at center cb, and line up your cue on the center line of the cb which is the shot line. The half tip just gives one the proper bridge placement for putting the cue on the shot line.