The average energy deposited per atom, 〈Ed〉=Ei(Ji/JMe), where Ei is the ion energy and Ji/JMe is the ratio of the accelerated‐ion to deposited‐thermal‐particle fluxes incident at the growing film, has been shown to be one of a set of parameters useful for describing the effects of low‐energy ion irradiation on film microstructure during ion‐assisted deposition. Recently, however, 〈Ed〉 has often been treated as if it were a fundamental, or universal, parameter. We have carried out experiments in which Ei (20–100 eV) and Ji/JMe (1–10) were varied independently during the deposition, at constant temperature, of polycrystalline Ti0.5Al0.5N films onto amorphous SiO2 substrates by ultrahigh vacuum reactive magnetron sputtering in pure nitrogen. Ion‐irradiation‐induced changes in film microstructure, texture, phase composition, and nitrogen‐to‐metal ratio were found to follow distinctly different mechanistic pathways depending upon whether Ei or Ji/JMe was varied, resulting in quite different properties for the same value of 〈Ed〉. Thus, 〈Ed〉 is clearly not a universal parameter.