We show that when elastic scatterers are present, the scattering frequencies may markedly differ from the one evaluated for plane wave states for the in-plane motion at the Born approximation. This feature results from the disorder-induced spatial localization of the eigenstates in the layer plane. The scatterer location dependence of the scattering frequencies is also discussed. At low concentration the in-plane localization is found to increase the inter-subband scattering.