It’s a bit offtopic, and only you see the full picture, but why backup windows image offsite? There is a lot of transient garbage that wastes space and bandwidth, ultimately causing important data to stay unprotected for longer.
Why not backup only user data, pull from the server that runs duplicacy? Or better yet, run duplicacy on each windows host, backup to the single target on your server, and copy revisions to b2?
Or if those are mobile windows PCs — backup to both, b2, and your server.
Duplicacy provides so much flexibility, compromise can be drastically improved.
Again, feel free to ignore this, it’s your setup, if it works — it works.