Unabsorbed sample. As reported in Sect. 3.2, the UV and the X-ray intrinsic luminosities can be affected by the presence of gas and dust along the line of sight. To improve the reliability of our analysis, we thus identify a threshold in the neutral absorber column density (i.e., N_H < 5 × 10²⁰ cm⁻²), which ensures that the AGN observed α_ox (i.e., potentially affected by absorption and reddening) are closer to their intrinsic values. Panel a: Cumulative curves of the neutral column density observed for the SUBWAYS (in red), T10 (in blue) and C21 (in black) samples. The dashed line indicates the adopted threshold above which the α_ox is considered significantly affected by absorption and reddening. Panel b: Expected deviation from ${\alpha }_{\mathrm{ox}}^{\mathrm{int}}$ = -1.5 as a function of the neutral absorber equivalent hydrogen column density, N_H. This plot highlights how absorption and reddening affect the observed α_ox. The dashed lines highlight the adopted thresholds, which help define a maximum neutral N_H and the corresponding expected deviation from the intrinsic α_ox, above which the observed α_ox cannot be considered reliable.