Properties of radio wave reflection from an optically thick, plane monotonic layer of ionospheric plasma with random density irregularities are considered by investigating numerically the influence of multiple scattering on the angular distribution and the integral intensity of the reflected signal. We use an improved solution of the radiative transfer equation in the approximation of small-angle scattering in invariant ray coordinates (SASIRC). The case of midlatitude ionosphere conditions is treated in most detail, but some conclusions about latitudinal dependence are also obtained, for both vertical and slightly oblique sounding cases. Conclusions from earlier versions of the theory showing a strong anomalous-attenuation effect are confirmed, with adjustments of the quantitative results. We describe a special amplitude calibration procedure for estimation of anomalous attenuation in practical experiments using dynasonde techniques, and discuss the application of our results to an explanation of ionogram spread F.