I must not have explained what I'm talking about well enough, because it seems like your response addresses something else entirely. I'll try again.
Let's say we're cutting to the left with a
3/8-ball aim. The proper shot (ignoring throw) is to send the center of the CB at a point 9/32" (1/8th of a ball diameter) outside the right edge of the OB. Your recommendation for that shot is to align the tip/ferrule/stick "flush against the outside edge of the object ball."
When CB/OB separation is fairly
small (balls close together), the balls appear to be about the same size. And the width of the cue tip or ferrule appears about the same size relative to each ball. So when you point the left edge of the tip at the right edge of the OB, you're also pointing the center of the tip a half-tip outside the OB edge. And, for tips of a normal size on pool cues, half a tip is not too far from the desired aim of 9/32" outside the OB edge. So your recommendation, to aim the left edge of the tip at the right edge of the OB, works for many of those 3/8-ball-aim shots, and all is well.
But now consider what the picture is when the CB/OB separation is
large (balls far apart). The OB looks much smaller than the CB, and the tip, relative to the OB, appears to be much larger. The apparent width of the tip/ferrule from shooting position behind the CB might even appear to be nearly as wide as the OB. So if you aim the left edge of the tip or ferrule at the right edge of the OB, where is the center of the tip/stick pointing? It's pointing much more than 9/32" outside the right edge of the OB. And that means you'll
overcut the shot.
Aside:
- In fact, aiming the inside edge of the tip or ferrule at the outside edge of the OB is an approximation method some people use for real thin cuts at long distances. Why does that work? It works because the center of the ghost ball for extreme cuts is nearly a half ball off the edge of the OB. And when you aim the side of the tip/ferrule at the edge of the OB, you are essentially also pointing the center of the tip/ferrule at approximately the center of the ghost ball -- just where you need to! However, it's just an approximation for accurately aiming CB edge to OB edge (or tip/ferrule center to ghost ball center), and its effectiveness should vary as the apparent widths of the tip/ferrule and the OB change with changes in the amount of CB/OB separation.
For cutting to the left with a
5/8-ball aim, the proper shot (again ignoring throw) is to send the center of the CB at a point 9/32" inside the right edge of the OB. Your recommendation for that shot is to align the tip/ferrule/stick "flush inside the edge of the object ball." As before, this works pretty well when the CB/OB separation is small. But when the separation is large, you're really aiming the center of the stick more than 9/32" inside the right edge and you'll
undercut the shot.
[Now, I imagine one's eye position can have an effect on these perceptions and how to handle the distant shots, but I think the effect I discussed will be pretty standard.]
And note that the effect I'm talking about does
not apply when simply aiming the center of the stick at something like the quarter points on the OB or the edge of the OB -- the tip still looks very "fat" relative to the distant OB, but the center of the tip is still pointing at the same place no matter how fat it is. But aiming with the edge of the tip can drastically change where the center of the tip is pointing depending on how "fat" the tip is relative to the OB.
