I can’t find the thread, but I remember a VEXU team that did a reveal a little bit ago (maybe someone could post a link to it) . They had a 3d printed hoop mounted at the nozzle of the flywheels. To me, this doesn’t seem like it would do much with the speeds we are dealing with, but I cant find any information on the purpose of it. I could see it helping with accuracy by causing more air pressure on the edges where the ball is closer. It could then maybe correct the course of the ball.
I believe that you are talking about this:
I think that these “nozzles” are to make sure that there is no vertical or horizontal variation between each shot making the shots more accurate.
The hubs ensure that the ball trajectory does not deviate from its angle since at the moment of contact with the flywheel, the ball is also kept in place by the hub. Though depending on the design of the flywheels, the curves of the wheel pmuch already ensure the ball will fly straight and center. Of course, that’s assuming that the flywheels are moving exactly or relatively close to the same speed.