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In this paper we consider the numerical problems faced by a blind dereverberation algorithm based on a multi-channel linear prediction. One hypothesis frequently incorporated in multi-microphone dereverberation algorithms is that channels do not share common zeros. However, it is known that real room transfer functions have a large number of zeros close to the unit circle on the z-plane, and thus many zeros are expected to be very close to each other. Consequently if few microphones are used, the channels would present numerically overlapping zeros and dereverberation algorithms would perform poorly. We study this phenomenon using the previously reported LInear-predictive Multi-input Equalization (LIME) algorithm. Spatial information can be used to deal with the problem of overlapping zeros. We describe the improved dereverberation performance that we achieve by increasing the number of microphones.