L_X−L_UV−υ_fwhm plane seen edge-on. Both optical and X-ray luminosities have been normalised to 10²⁵ erg s^-1 Hz^-1. The υ_fwhm values are taken from S11 and are normalised to 2000 km s^-1. Here we considered the υ_fwhm estimated from the whole Mg ii emission line. The bottom panel shows the residuals defined as the difference between the observed monochromatic X-ray luminosity at 2 keV and the best fitting function.