I also would have thought that the blades centerline would be more inside the shroud, not at the halfway mark. It is a PULL system, and one would think that the more the blade center was inside the shroud lip, the more PULL it would create. Perhaps common sense does not prevail in this particular example.

However, speaking in scientific terms, the blades are indeed modeled to have a vortex point, a point at which as they spin their front area of each blade PULLS and their rear area of each same blade creates a PUSH to the rear.