Evolution of the Hα (upper panel) and Hβ (lower panel) lines for SN 2020acat (red) and the JEKYLL models (black) with an initial mass of 17 M_⊙, strong mixing and strong expansion of the radioactive material, and a mass of hydrogen in the envelope of 0.0135 (left), 0.027 (middle), and 0.054 (right) M_⊙. Spectra from nine logarithmically spaced epochs are shown, and the model C/O-He (blue) and He-H (red) interface velocities are indicated with dashed lines.