Fits to stacked spectra (from “spec-z” sample) in equally sized bins of α_ox (top panels) and L_UV (bottom panels). The legend gives the mean value of each subgroup, the number of stacked sources, and the fitting statistics. The soft power law (green) and the hard power law (blue) as well as the sum (black) are shown. Each curve is the best fit to a bootstrap realization of the sample. In the top panels, from the left to right panels, the green curves move upwards. The strengthening of the soft excess is quantified by q with error bars, increasing from 0.13 to 0.58. The bottom panels show fewer changes in the green warm corona component with L_UV.