Confidence contours of ratios between fundamental CRSF parameters, “10 keV feature”, and continuum flux correlations. For all flux-resolved spectra, the best-fit values are marked with a cross. The dotted lines show the 3σ contours, and the solid lines indicate the 1σ contours for the N1 (red) and N2 (blue) observations, respectively. The black points mark the best-fit values from the flux-averaged dataset, while the shaded regions in the left panels (N1 in red and N2 in blue) highlight the uncertainties of the averaged best fit, as given in Table B.1.