Top panel: optical (left) and near-infrared (right) [Ni II] line profiles at 190 d past explosion in the high-luminosity models DDC0 (M_Ch; thick solid line) and SCH7p0 (sub-M_Ch; thin solid line). The dotted lines show the impact of artificially decreasing (increasing) the Ni II/Ni III ratio on the emergence of [Ni II] lines in the M_Ch (sub-M_Ch) model. The near-infrared (NIR) line profiles were normalized to the same mean flux in the range 1.87−1.88 μm; the optical profiles are not normalized. Bottom panel: same as above for the low-luminosity models DDC25 (M_Ch; thick solid line) and SCH2p0 (sub-M_Ch; thin solid line). We note the absence of an optical [Ni II] 7378 Å line in the sub-M_Ch model with high Ni II/Ni III ratio see text for details).