Does multicast frequency effect over replication clean up?

Increasing the multicast frequency will provide HP with more streams to process per HP cycle. This will yield more trimmed over replicated streams per HP cycle but will slow the HP cycle time.  Having Overlay Index active will help clean up over-replicated streams as well.  You can temporarily reduce the minimum nodes required for it to become active (32 nodes is the default) to enable the feature in your cluster.