An H-R diagram for AGN?

We have been searching for a correlation space that provides an optimal discrimination between the diverse classes of AGN. A space involving FWHM Hβ, the ratio of EW FeII/EW Hβ and soft X-ray spectral index shows the strongest discrimination and intercorrelation. It represents a synthesis of several correlations that have emerged in the past decade. We interpret the correlations as driven primarily by orientation and L/M ratio of the central source with an uncertain role for Fe abundance.