Kolmogorov–Smirnov probability as a function of the σ threshold used to switch to a more complex intrinsic spectral model (results obtained starting from EPWL and ELP models are coincident). The results were obtained by using the EBL model of Gilmore et al. (2012) and different starting spectral models, as discussed in Sect. 4.2. Dotted vertical lines at 1.8 and 2.2 correspond to σ values used to estimate the systematic uncertainties due to the model selection (see text for details).