The cushion mount if installed correctly will allow your mounting ring to easily drop over it, allowing room for the projections on the disposer to fit into. Looking at the Sink flange you will see a lip below the groove at the very end of the flange.

Note: If the cushion mount is installed correctly the lip at the end of the flange will be fitted into the groove, in the cushion mount.
Examples

Posted in: Disposer Installation