A comparison between the nebular spectra of SN 2023ixf (which have been smoothed with a Savitzky–Golay filter to reduce noise) and the 12, 15, and 19 M|$_\odot$| nebular spectral models of Jerkstrand et al. (2014) (J14). The plots on the left show the day +291 and +342 spectra of SN 2023ixf compared to the J14 models scaled using equation (11). The plots on the right show the day +291 and +342 spectra of SN 2023ixf compared to the J14 models scaled using the additional term in equation (2) to account for the incomplete trapping of |$\gamma$|-rays.