about 20 years ago, the existence of the X-ray Baldwin effect has been confirmed by several works performed with the highest spectral resolution available at X-rays. So far, several possible explanations have been proposed. @Jiang:2006vn argued that the observed anti-correlation could be related to the delay of the reprocessed radiation with respect to the primary continuum. The response of the circumnuclear material to the irradiated flux is not simultaneous, and one should always take this effect into account when performing studies of reprocessed features as the iron K$\alpha$ line or the Compton hump. @Shu:2010zr [@Shu:2012fk] have shown that averaging the values of $L_{\mathrm{X}}$ and $EW$ for all the observations of each source results in a significantly flattened anti-correlation. However, by itself variability fails to fully account for the observed correlation [@Shu:2012fk].

Explaining the X-ray Baldwin effect with a luminosity-dependent covering factor of the torus
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A mechanism often invoked to explain the X-ray Baldwin effect is the decrease of the covering factor of the molecular torus with the luminosity (e.g., [@Page:2004kx], [@Bianchi:2007vn]). The decrease of the fraction of obscured sources with the luminosity has been reported by several works performed at different wavelengths in the last decade, although some discordant 