Hey RMan,
Adjust height of a custom (add new) Flat Truss to fit your needs. Set the Support Height to a few inches lower than the Building Locations height for the floor involved.
For default Builidng Location Ground Floor height of 1′- 5 1/2″, I set Flat Truss Support Height to (minus) -1′-7″.
If you change Flat Truss height , the minus Height will also need to be changed. But once set, it should work that location without adjusting the height setting.
Jack zimmerdesign.com