The solution obtained with the acoustical image sources method was shown to be the contribution of terms issued from a series development of the integral method (believed to be the exact solution). Missing terms in the geometrical method represent, among others, the contribution of diffraction. Taking all of them into account would indeed lead back to the full integral method. Alternatively, would it be possible to consider only a subset of these terms, therefore adding missing information to the geometrical method? This would bring the latter to its much-awaited role in the medium-frequency range.