Ratio of the pseudo-equivalent widths of the HV and PV components against the photospheric velocity of the Si IIλ6355 feature for the low-bias sample of 190 SNe. For objects with multiple spectra we take the mean value in both dimensions, treating the uncertainties with the ASYMMETRIC UNCERTAINTY package (Gobat 2022). The vertical dotted line indicates the 12 000 km s⁻¹ cut velocity at maximum light between the NV_W (red) and HV_W (green) SNe Ia.