Since the sinker versus 2 seam fastball post is pretty ugly, I wanted to ask my question under a new topic.
Has anyone heard of throwing the fastball with the fingers off the seams in order to get movement? I am talking about both fingers being totally off the seams.
For most people, the seams are used to help create movement not takeaway from movement. The seams actually create resistance against the air that make the ball move. For example, a person who throws a four seam fastball will tend to have more movement than a two seam fastball. Therefore, you will generally find more movement by using the seams and pressing against them in various ways.
With this said, many pitchers will have natural pronation or supination in their delivery that creates movement regardless of how they grip the ball. This is why it may be that some pitchers look like they are getting more movement even if they are putting much emphasis on using the seams. My suggestion is you stick with using the seams to develop movement. Over time in your practices, you will start to notice what emphasis of pressure works best for you.