Influence of the underlying source distribution on the astrophysical constraints derived from the clustering analysis. The confidence contours (see Fig. 6 for colour meaning) are extracted from the analysis of a typical data set of 50 events above an energy threshold of 60 EeV, built from a typical realization of the reference model (n_s = 10^-5Mpc^-3, δ = 5°), indicated by a cross, assuming either an a priori uniform source distribution (on the left) or an anisotropic distribution (on the right) similar to that of the galaxies (see text).