Results are presented from measuring nuclear modification factors RAA of the π0, η, KS, and ω mesons produced in systems of Cu + Au and U + U collisions at cms energies of $$\sqrt {{{s}_{{NN}}}} $$ = 200 and 192 GeV, respectively, in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). The RAA values are found not to depend on the type of neutral meson and to vary in the ~0.4–0.6 and ~0.2–0.3 intervals for central Cu + Au and U + U collisions, respectively. The mean RAA values for different collision systems (Au + Au, Cu + Cu, Cu + Au, and U + U) are found to coincide within the measuring errors when estimated at comparable values of collision energy $$\sqrt {{{s}_{{NN}}}} $$ , and of the number of nucleons participating in a nucleus–nucleus collision, Npart.