Analysis of the f_X − f_UV relation in redshift bins. Top panel: slope γ as a function of redshift. The slope stays around the reference value of 0.6 for the entire redshift range explored. Bottom panel: dispersion as a function of redshift. The dispersion stays around the median value ∼0.25 dex, showing a decreasing trend with redshift. This is easily explained by the fact that, at the highest redshifts, only pointed, dedicated observations, unaffected by the observational issues characterising serendipitous observations, are available. Both intrinsic dispersion (output of the emcee regression analysis) and observed one are shown.