Impact of uniform mixing on the optical (left) and near-infrared (right) [Ni II] line profiles at 190 d past explosion, using the same models as in Fig. 8. Also shown are observations of SN 2017bzc at a slightly later phase (+215 d past maximum) scaled to match the mean flux of the original profile in the range 7600 − 8000 Å and 1.83 − 1.91 μm, respectively (grey line). The feature marked with a ‘⊕’ at +8000 km s⁻¹ in the optical spectrum is due to absorption by the Earth’s atmosphere (A-band).