Frankly I don’t really have an answer to this question, because I have also struggled with client settings here.
What I have found though is that setting partitions/directories for an image backup is done by the client in settings> image backups. But apparently you don’t enter partitions/directories in settings>file backups!!! No, I had to enter these in a separate window Add/Remove Backup Paths. If on the server settings you allow the client to change these, when you enter these paths at the server these are the locations the settings turn up in at the client (after about 3 to 5 mins). And when you change server settings the client settings will change shortly after.
I havn’t tried changes such as what changes at the client end affect the server settings and much beyond this for now, but this much does work. Either way, it doesn’t really seem very intuitive to me.