It is shown that st simple scaled Hartree-Fock (ScHF) model describes very well the ring proton affinity (PA) of a vast variety of polysubstituted benzenes, naphthalenes, and biphenylenes. Its utility in predicting PAs of large alternant aromatics is illustrated on pyrene and monofluoropyrenes. The calculated PAs are in accordance with the available experimental evidence providing at the same time useful complementary information. Finally, it is found that PAs in polyfluoropyrenes follow the same simple additivity rule, based on the independent substituent approximation (ISA), which was observed earlier in smaller alternant aromatic systems. The origin of the additivity property of the proton affinity is briefly discussed.