I've got it working!
All the faffing with static IP address, 2.x.x.x addresses etc all unnecessary. It's the order of starting FS and Enttec Pro Manager which makes the difference. I got to the bottom of it using ArtNetominator which is less finicky on the order then once I could see ArtNet traffic I knew I was on a winner.
I just used the existing DHCP address of 192.168.1.118 and FS configured to:
0, 0, 0
Start Enttec Pro Manager
Start record in Enttec Pro Manager Standalone tab
Run some some scenes in FS
It works, phew