Using one of the generic models (CO oxidation on Pt with surface-oxide formation) predicting kinetic oscillations in heterogeneous catalytic reactions, we show that the efficiency of two-variable periodic perturbations with respect to converting natural period-1 oscillations to period-1 oscillations at the forcing frequency is remarkably sensitive to the kind of perturbations used. "Counter-phase" perturbations are much more effective compared to "in-phase" perturbations. The physics underlying these findings is suggestive of their applicability to many other models and/or real systems exhibiting kinetic oscillations.