The wording in the command line is confusing and potentially misleading…
When the “RollingBall” option is selected the " “radius” in the command line refers to the radius of the rolling ball.
When the “DistBetweenRails” option is selected the “radius” in the command line refers to the distance between the rails.
When the “DistFromEdge” option is slected the “radius” in the command line refers to the distance from the edges of the input surfaces to the edges of the blend.