It is well known that the statistical effects of long-range signal propagation in random channels generally lead to considerable degradation of both the signal coherence and the array output. In random-inhomogeneous underwater sound channels, these effects are of a primary importance if a large horizontal array is used for high-resolution operation in spatial domain. The key physical effect in such a scenario is known to be the range-dependent cross-modal coherence loss caused by multiple sound scattering by random channel inhomogeneities, both volume and windy surface ones. In this pa-per, we demonstrate numerically how and why the horizontal array output dramatically degrades if the received signal consists of a large number of partially-correlated normal modes. From the point of view of general statistical antenna theory, the results present-ed are considered to be a further development, with application to the multimode transmission channels.