Moving files will always be an add and remove, but as all blocks inside the new file are the same as in the deleted one, syncthing on the receiving side knows that it can move the file as well.
I never used IgnoreDeletes myself, so I didn't know how it handles moves/renames.
Did you try trashcan versioning?
If you set the MacBox to send-only, and enable versioning (not trashcan) on you unRaid device, you can have a revisioning system, which could be enough "backup", as you can have multiple versions of the files (if you have enough space there). I don't know how moves are handled by versioning either .