Indexer as rollers:

I have seen many top teams using rollers as their indexer, but I was wondering how to place the roller perfectly so that when the discs is being pushed by the roller, the disc wouldn’t change its angles. And also, I know that using flywheel weight can help the discs to shoot longer but how much distance is needed for the roller to the flywheel in order to have the same amount of time as pneumatics?