Long term averaged values of the electron irregularity drift velocity in the auroral electrojet obtained from VHF radar studies at Siple, Antarctica, show that the magnitude of the observed drifts is strongly range dependent. This feature is explainable in terms of the dispersion relation for the irregularity generation process, which shows that the observed irregularity phase velocity is strongly dependent on the angle between the radar beam and the earth's magnetic field. Although major features of the variations of observed drift velocity with range can be accounted for by taking this aspect angle dependency into account, best agreement between the theoretical and observed curves is obtained by assigning relatively large values to the electron collision frequency at 105 km.