The Schoenberg-Muir averaging technique is a powerful method for calculating the bulk properties of layered and fractured elastic media. The theory is exact only for infinite layers and infinitely low frequency waves. It is already known that the approximations are accurate for infinite flat layers if the wavelength of the slowest elastic wave is long enough to contain a representative sample of the layers at any position in the medium. In this paper we run models testing the infinite flat layers assumption. We find that if the layers are much longer than they are thick this approximation is a good one and Schoenberg-Muir averaging is applicable.