To improve the performance of multi-channel speech enhancement algorithms, we previously proposed a hybrid Wiener post-filter for microphone arrays under the assumption of a diffuse noise field [4]. In this paper, considering the speech presence uncertainty, we further improve the hybrid post-filter presented before by integrating a novel robust estimator for the a priori speech absence probability, which makes full use of the correlation characteristics of the noises on different microphone pairs and hence offers the much more accurate speech absence probability estimates. The effectiveness of this improved hybrid post-filter was finally confirmed by the experiments using multi-channel recordings in various car environments.