Ni II/Ni III population ratio at 190 d past explosion for the high-luminosity models DDC0 (M_Ch; thick dashed line) and SCH7p0 (sub-M_Ch; thick solid line) as well as the low-luminosity models DDC25 (M_Ch; thin dashed line) and SCH2p0 (sub-M_Ch; thin solid line). Regardless of the luminosity, Ni III dominates in the sub-M_Ch models all the way to the innermost ejecta (≲3000 km s⁻¹), whereas Ni II dominates there in the M_Ch models.