The Effective Medium Theory used to describe the magnetic properties of randomized heterogeneous materials includes as parameters the intrinsic permeabilities µi of the magnetic particles and an effective shape factor Ñ. This paper compares the experimental variations of Ñ to the theoretical variations predicted by an EMT. It is shown that the effective shape factor Ñ cannot be seen as the mean shape factor of the composite components. The values of Ñ belong to the range ]0,l/3[, and are strongly correlated to the permeabilities µi. In the low concentration range, random distributions of needle-like and flake-like particles both lead to low values for Ñ. The result Ñ=1/3 is obtained in the whole concentration range only in the case of randomly dipersed spheres. The values of the µi might be kept constant up to a volumic fraction c in magnetic matter equal to 50%, according to previous results we got. The experimental results presented here are weil described by this theory up to c=50%.