Maybe this is straight forward:
When you define a shared folder in the GUI, you specify the location of a shared folder.
Lets say this folder is /srv/device-by-label-A/USERS/userA and userA logs on.
User A can then also view any content above his shared directory (so he can see everything in /srv/device-by-label-A/USERS).
The GUI does not seem to provide a way, or does it?
I could chown all higher directories to e.g. root and chmod 0700 but is there a better way?