R_X vs. 1.4 GHz luminosity color-coded by the AGN fraction (f_AGN) of COSMOS (circles) and XXL-S (diamonds) XQSOs. Radio loudness threshold in radio luminosity as defined by Miller et al. (1990) is shown with the black dash-dotted vertical line, while the radio-to-X-ray radio loudness threshold from Pierce et al. (2011) is shown with the black dashed horizontal line. It can be seen that both RL thresholds miss a significant fraction of sources where the AGN dominates the radio emission.