Understanding Delete Orphans Policy

I'm struggling with my understanding of the 'Delete Orphans' feature within CTA, and how best to apply a good 'Delete Orphans' policy.

We have CTA/VE version9.0 being used to archive content from VNX to Centera. All file data hosted on the VNX is subject to a backup policy with 6 months retention. We therefore want to guarantee that any deleted stubs can be restored under this policy and still connect to the associated Centera tier file content.

Reading the CTA documentation would suggest that a 'Delete Orphans' policy can be configured to keep Orphaned files (files with a deleted/missing stub) for a period to match the backup policy, and longer that the default 30 days. Therefore the CTA would protect the file content with missing stub from being deleted by Centera for the duration of the 'Delete Orphans' policy.

The two main points I am struggling with are;

• It's clear in the CTA GUI that you can create a 'Delete Orphans' policy, I can't understand why it needs to have a Rule attached to the policy, and what a good rule would be that will add the protection universally to all orphaned content??
• Also, I think that the 'Stub Scanning' process is used to detect missing stubs, and therefore mark files as orphans. The documents i have read to date provide conflicting information about when the stub scanner runs - but the CTA GUI would suggest this happens on the 15th of every month @1800hrs. So, when, and how often should the 'Delete Orphans' policy be scheduled