Is a 9.1 HCM to 9.1 CRM Employee Data integration overview available?

Is a 9.1 HCM to 9.1 CRM Employee Data integration overview available?

We would like to know how the delivered sync messages are designed from a data object perspective.  i.e. what fields/components are integrated and used with these EIPs.  I've found some redpapers, but nothing high level that will speak to the integration as a whole.  We've noticed that any change to a federal PAR results in a message being generated, even if that PAR doesn't change any PIA (front end) facing fields that you would find on the Worker.  I'm being asked "why does it do this" and I can't give any anser better than, "it sends everything... just in case".