  In this second paper in the series, we carefully analyze the observational
properties of the optical FeII and NIR CaII triplet properties as well as the
luminosity, black hole mass, and Eddington ratio in order to define the driving
mechanism behind the properties of our sample. Most of the significant
correlations are associated with CaII triplet. The CaII shows an inverse
Baldwin effect, bringing out the particular behavior of this ion with respect
to the other low-ionization lines such as H$\beta$. We also performed a
Principal Component Analysis, where $\sim80\%$ of the variance can be explained
by the first three principal components drawn from the FWHMs, luminosity, and
equivalent widths. The first principal component is primarily driven by the
combination of black hole mass and luminosity with a significance over
$99.9\%$, which in turn is reflected in the strong correlation of the first
eigenvector with the Eddington ratio. Since the observational correlations are
better represented by the Eddington ratio, this could be the primary mechanism
behind the relations observed in our CaII-FeII sample. Since the calcium belong
to the $\alpha$-elements, the FeII/CaII flux ratio can be used as a chemical
clock for determining the metal content in AGN and trace the evolution of the
host galaxies. We confirm the negative enhancement of the ratio FeII/CaII by
the Eddington ratio, suggesting a metal enrichment of the BLR in
intermediate-$z$ with respect to low-$z$ objects. A larger sample, particularly
at $z>2$, is needed to confirm the present results.
