I synchronize eM Client using Fruux.com, which provides CardDav support for my contacts. It works fairly well, but some fields, e.g., Related People do not appear in eM client. I would love to have the schema match the CardDAV schema more closely, if indeed that is the source of the issue.
I completely aggree!
For example, if I assign a Related Person the iOS label “Child,” it does not survive sync via Fruux.