Result of the fit of the (singular) power-law model to the composite model for 20 different sets of complex sources. For each realization of the complex source, we show the value of the logarithmic slope γ′ (circles) of the fitted power law as a function of the position of the inner-most lensed image in the system (x_min). The time-delay ratio is also shown (star-like symbols). The color code shows the (non-reduced) χ² obtained for the fit of the power-law model; the typical number of degrees of freedom is ~30.