Total luminosity in the first overtone of CO, for models with different χ values (lines), compared to observations of stripped-envelope supernovae (data taken from Gerardy et al. 2002, Hunter et al. 2009, Ergon et al. 2015 and Rho et al. 2021). The observed values are scaled with the difference in ⁵⁶Ni mass between the model and the SN. For SN 2000ew there is no observational estimate of this so the scaling factor is set to 1, with an error bar of factor 5 attached. The error bars indicate the uncertainties in the ⁵⁶Ni mass when such are reported. There is no reported error for SN 2020oi, so it was arbitrarily set to be a factor 2.