In this work, we consider the single ionization of Ar by 200 eV positron and electron impact. The quantum mechanical continuum distorted wave (CDW) model is used in the one-active electron approximation. Parametrizations of Hartree-Fock potentials by Garvey et al. Are used to represent the interaction of the light particles with the Ar+ ion. The post collisional interaction (PCI) between the emitted electron and the receding projectile is naturally considered by the present model. Comparison with recent experimental data for very asymmetric geometries is made. The role of the PCI is studied by analyzing the differences in the angular distributions for positron and electron impact predicted by the CDW model and the first Born approximation.