Distributions of EM as a function of electron temperature (kT_e) and ionization timescale (τ = n_et) at the labeled times for models B18.3 (upper panels) and B18.3-Dec (lower panels). The panels present three-color composite images of the EM distributions, where different colors represent contributions from distinct shocked plasma components: shocked CSM (red), shocked material from the H envelope (green), and shocked Fe-rich ejecta (blue). White contours highlight the regions dominated by Fe.