An area of grey would seem to be 'at maximum flow rate posible'. Under what conditions? How do you size the header pipe. Same size as the valve? Run as long as you want?
Just to through it out there as food for thought,and I haven't dealt with AF systems in a while, but might it be an option on some of these buildings with alot of AF systems, to swap out the big DDCA at the supply for a RPZ and change the existing small AF RPZs for swing checks with 3/32 orifice. The cost might be offset in certain cases with not needing to retro fit multiple test headers and reduce testing costs in the future. Obviously actual valve takeouts and availability need to be verified.