Hi Markus,
If you have your "Staff Directory Info" records in one place, and your fe_user in a "Storage Folder", that can work. You can specify both folders in StartingPoint. If you put them both in the main Storage Folder, that should work too.
To give the pid of the Storage Folder to Staff Directory, you edit the Flexform for the Staff Directory and on the Main tab, select Startingpoint and choose the folder there. You can choose multiple folders too.
You can also specify the storage pid list in TypoScript -- in the Setup of the extension template -- by adding plugin.tx_wecstaffdirectory_pi1.pid_list = 123, where 123 is the pid# of the storage folder. For multiple, you use comma -- 123,234,345
If you are still stuck, let me know where the Staff Directory Info records are?
-Dave