Per Table 5-2, for "wetted" double butt joints only spot or full radiography is permitted, and thus only 85% and 100% joint efficiencies are used.
For roof double butt welded joints I believe the --, Spot, Full in the Radiography column are meant to be lined up with 70%, 85% and 100% in the efficiency column. Thus in a roof 70% joint efficiency is no radiography .