1. Use keys (which represent the transfer root) for greater clarity
2. Exclude needs to be relative to the transfer root
3. Make sure you’re using rsync exclude syntax properly!

For example, I have a RsyncShareName /service, under which is a chroot environment containing /proc, /var/lib/mysql etc. I want those folders to exist in my backup, but not their contents (for obvious reasons). Therefore, I made a BackupFilesExclude key /service and for it I added /proc/** and /var/lib/mysql/**. Works as intended.