Chuck, thanks for the reply.
Using the airplane as an example, would the following be a correct assumption of what you have said?
The above photo shows a pair of tip vorticies. While these vorticies are growing in diameter, their centers are moving toward each other. In other words, the horizontal distance between the centers of the vorticies is contracting.
On a hypothetical rotor with blades that had their root cutouts at 80% of rotor radius, the root vortex would be at 0.8R and the tip vortex would be at 1.0 R. The airfoils, which are located between 0.8 R and 1.0R, would produce a wake similar to that of the airplane in that the horizontal distance between the centers of the root vortex and the tip vortex would contract.
Dave