Imagine a pinpoint contact point on the radius between your tipmand the cue ball. Given different radius tips, the flatter the tip the further from center you need to hit to place the pinpoint on the radius at the same place on the cue ball.
The further out you hit, the more deflection. Regardless of the shaft being standard or lower deflection, the further from center the more deflection, which, is more variable.
Understanding that, why would a flatter tip, requiring more extreme off center hits for the same spin transfer, ever be preferred?
As far as shaft diameter is concerned, the dime radius on an 11.75mm tip is the same as the dime radius on a 13mm tip. The radius defines the curvature, not the diameter.
Pretty straight forward stuff...
I won't even get in to the concept that a good stroke, dime radius and close to center hit makes the standard solid maple shaft superior to a glued together pie of wood that is almost as much glue as it is wood. Oh shit... I went and did it there.
Personally, I prefer a 'flatter' tip with the edges just softened or 'rounded'. That way I can better define just where on the cue ball I will be hitting(or at least targeting to hit). Another reason I prefer that shape is because I prefer a soft tip & when hitting on the edge & that soft tip compresses on a high speed hit, it needs depth for the compression. Finally when I do want to hit center CB there is a bit more room for a slight off center placement to still make contact with the center.
Again, all of the above are JMHOs.