From the New York Times:
In the first week of spring training, Small gripped a ball along the seams that frame the sweet spot. That, he explained, was how he used to throw a sinker. Last spring, the pitching coach Mel Stottlemyre suggested that he move his fingers up a bit, so only the right one rested on a seam.
The effect was astounding. If Small made a mistake, the ball would sink a little. If he didn’t, the ball would sink a lot, darting away from a left-handed hitter. It was a revelation, and the Yankees liked what they saw.