Measured Hα (top left) and Fe II 5169 Å (top right) line velocities of SN 2021aatd compared to those of SNe 1987A (Xiang et al. 2023), 2020faa (Yang et al. 2021), and Type IIP 2012aw (Bose et al. 2013). The calculated line velocities from a3, a4, and a5 explosion models of Dessart & Hillier (2019) (DH19), as well as photospheric velocities of SNe 2021aatd and 2020faa determined from our SYN++ models, are also plotted (see text for further details). Bottom left: Calculated photospheric temperatures (T_phot) from DH19 a3, a4, and a5 models compared to T_phot values of SNe 2021aatd and 2020faa determined from our SYN++ models. Bottom right: Calculated V-band absolute magnitudes (M_V) from DH19 a3, a4, and a5 models compared to the measured values of SN 2021aatd.