By smaller I assume you are talking about the curvature, given that the size of the tip is held constant.
So stroke errors would be magnified w/ a smaller tip?
A shorter radius on the tip puts more english/draw/follow per unit of offset from dead straight onto the center of the cue ball. Which is great if that is what you want, and not so much if you did not want so much. So the contact point error (where you wanted to hit the cue ball minus where you actually hit the cue ball) is part of the equation. Those with very pure strokes can get away with shorter radii; while we of more average capabilities cannot get away with it often enough.
It makes sense that if less of the tip is coming into contact with the ball, there would be greater pressure and it would be easier to achieve spin. I guess that also means that you definitely could impart a lot of unwanted spin if your stroke is not pure...but that is true with any tip if you have a poor stroke.
With a given hardness of the tip, and a given speed of the stroke, the tip will deform to create an area of contact that is independent of the radius of the tip (first order).
Consider the extremes of tip radii: An absolutely flat tip will not impart draw/follow/english no mater what the offset. A tip with a very small radius (say 1/2 a dime) will miscue very easily at little offset. So, something in the middle is prescribed.
So how did you arrive at the size you use currently? I guess I will really have to try smaller tips to see if I can feel the difference compared to what I'm currently using. Maybe once my games improves a bit and I have some time or more cues to mess around with
My cue came with a nickle radius tip. I played with it for a couple of weeks. Then, I took a nail file and decreased the radius towards a dime, played with it for a couple of hours. I was impressed with the added amount of english I could impart, and unimpressed with how easily (and how often) it would miscue.
I then, took the nail file and increased the radius a little, played with it again, and over a few trials and error sessions, I found out that a Nickle was a little dead on the spin side and forgiving of gentle massé, while the dime was imparting more spin than I really wanted and miscued more than I wanted. So, once again something in the middle was in order.
The above is not such a good tip-radii search strategy. A better strategy is to slowly decrease the radius until the cue starts to impart more spin and/or starts to miscue too often, then increase the radius just-a-tad until the tip is performing at your level of stroking. Your tips will last longer with this strategy than going all the way to a dime and backing back off.