Thanks for the suggestion @andreas-doehler, but in digging deeper I found that the example above worked, the problem was however with my hostnames. I had only now noticed that Proxmox VM Names have to be valid hostnames and my VM naming convention uses _.
The fix for my problem is Hostname translation for piggybacked hosts with the following regexes.
Piggyback via the “clone” host on the secondary site now works.