Actually, that is incorrect. There is a section of the F3A rules that specifically say that at local contests of 4 or more rounds that the F pattern can be used. Here it s,

Note 1: Final and semi-final flights to determine the individual winner are usually only required for
World and Continental Championships. For open international events, national championships, and
domestic competitions, the total of the three best preliminary flights may be used to determine the
individual winner and team placing. Further flights of Schedule F may be planned, depending on
local conditions and time available.