Optical plane of the E1 MS, FWHM Hβ_BC vs. R_FeII. Sources from our sample are represented as red and blue circles; the gray symbols represent the MS from the sample of Zamfir et al. (2010), with RL sources identified by an outer circle. The red circles are sources with the D parameter larger than 1.5; for the blue squares D ≲ 1.5. The horizontal dot-dashed line marks the limit between Population A and at FWHM = 4000 km s⁻¹ . Dotted lines separate spectral types and NLSy1s. The vertical dot-dashed olive line identifies the R_FeII = 1.2 limit for xA “safe” identification according to Paper I. Only one source qualifies as a true xA candidate. The position of the prototypical xA source I Zw 1 is marked.