Position of SN 2021tsz on the V-band slope (s₁) vs t_PT plot, alongside other SNe II. SNe II with photospheric phases shorter than 90 days are labelled, and this region is shaded in grey. SNe II with peak magnitudes fainter than −18 mag are marked with stars (⋆), while squares denote those brighter than −18 mag. The points are colour-coded by the absorption-to-emission ratio of Hα at 30 days. Data are compiled from the literature (Anderson et al. 2014a; Valenti et al. 2016; Gutiérrez et al. 2017a; Dastidar et al. 2024), along with independent estimates from this work. The right panel shows the histogram of the s₁ distribution for SNe II with t_PT < 90 days, where those brighter than −18 mag are shown in blue and those fainter than −18 mag in red.