Using data from the Middle and Upper Atmosphere Radar, we present a study of the subtle characteristics of the echo power distribution caused by aspect sensitivity at VHF wavelengths. This is accomplished by using 64 beam positions in order to create a high-resolution map of the echo power distribution close to zenith. It is shown that the maximum in the power distribution can be tilted away from vertical by as much as 1 degrees. Further, azimuthal scans of echo power show a wave-like structure possibly caused by the tilt of the echo power distribution. Justifications based on the characteristics of typical isentropic surfaces are used to explain an asymmetry between the zonal and meridional components of the tilt of the echo power distribution. Finally, the use of spatial interferometry to estimate the angular tilt of the echo power distribution is shown to be valid. In previous studies, it was assumed that the in-beam incidence angles, measured using spatial interferometry, are equivalent to the angular location of the peak in the echo power distribution. In the present work, we show this assumption is reasonable. (C) 1998 Elsevier Science Ltd. All rights reserved.