The administration area allows to set up custom properties for contacts etc.
However, it is not possible to use these additional entries to create custom reports.
Admin-created ("global") custom properties should show up in the "Conditions" and "Columns & Order" section.
At least, that is what I was expecting.
If the current behaviour is intended, please feel free to move this topic to the feature request section.
Greetings,
Thorsten