InP substrates were implanted with 120Sn, 115In and/or 31P ions and thereafter, with trace amounts of radioactive 111In ions. Following rapid thermal annealling, the fraction of undisturbed 111In sites was measured with perturbed angular correlation (PAC). Though Sn and In ions have comparable masses, undisturbed fractions of 42 and 67%, respectively, were experimentally determined as attributed to the charge on the ionised donor and differences in bond length. Precipitated Sn atoms were shown to have a negligible influence on the undisturbed fraction. Comparing In-, P- and In-and-P-implanted samples, excess P yielded a greater fraction of undisturbed sites relative to excess In (87 and 67%, respectively) as attributed to the lesser mass of P and hence, the lesser energy deposited in vacancy production. However, In-and-P-implanted samples yielded an intermediate value (81%), demonstrating the influence of non-stoichiometry. Also, complementary double-crystal X-ray diffraction measurements were in qualitative agreement with the results derived from PAC with the latter shown to be an effective analytical technique for the measurement of disorder in ion-implanted InP.