It's an interesting concept, and I've thought about aspects of concave tip sections previously. Even shaped concave edges to see if I could hit further off center, but rough experiments showed no benefit.
Some things to consider:
By shaping the center area of the tip in this concave shape, if one strokes say 2mm off CCB, it may work out that the tip actually contacts the CB at CCB.... hence, one might presume no spin.
But, in pivoting to the 2mm offset, the cue's travel direction will be different to the direction from bridge V to CCB, so the CB will travel to the right of the original aim and apply some, but not as much as usual spin, which with create some squirt to the left.
The degree to which this does this I'm not sure, but in effect, it will be a similar effect to playing with a shorter bridge length than one is used to.... because...
If one bridges within a couple of inches of their cue's effective pivot point for a shot, the line of CB travel remains almost identical if you strike the CB a couple of mm either side of CCB, as the change in cue direction via the pivot to offset, is almost identical to the resultant squirt angle. (Which is basically the definition of a pivot point.) So in many situations, this concave method adds a variable, rather than reducing one.
Keep in mind that this pivot is not about using aim then pivot methods to apply spin, it's the fact that hitting off center by accident, is actually a pivot (though it gets more complicated if one swipes severely or shifts the bridge during the stroke).
If one bridges considerably shorter than their effective pivot point, then a 2mm offset to the right of CCB will push the CB to the right significantly, which is what this concave method should also achieve.
Some think that unintended side leading to unintended throw is the biggest issue in aiming. I do not. There is much more variation in CB travel direction from inaccurate stroking when one bridges at a considerable distance from the effective pivot point for a shot.
Another thing to consider is that this concave method would interfere with one's judgement of applying gearing outside english, requiring larger offsets than usual.
There is the odd shot where spin induced throw is the main concern. e.g. A long straight shot with CB say 6 inches from the OB. In this range of shot, such a tip may be advantageous.
Don't take this as gospel, just thinking aloud and planting some seeds for thought.
Colin
