the result of not simultaneously changing the opacity with $T_{\rm exc}$ and/or non-local thermodynamic equilibrium effects. However, the [Ca$\,$]{} spectrum does not change significantly with $T_{\rm exc}$ and other model spectra show the same relation between [Si$\,$]{} $\lambda 3858$ and [Si$\,$]{} $\lambda 5972$ [e.g., @Kasen07:asym; @Blondin13]. We therefore consider the qualitative changes in the spectra to be correct, although the corresponding temperatures may not be. All models show that the strength of [Si$\,$]{} $\lambda 3858$ and [Si$\,$]{} $\lambda
5972$ are anti-correlated; we will use this relation as the primary model prediction. We will later use $\mathcal{R}$(Si) as a proxy for light-curve shape.

The excitation energy for the various [Si$\,$]{} lines also explain the correlations between the various [Si$\,$]{} features. The [Si$\,$]{} $\lambda 3858$, [Si$\,$]{} $\lambda 5972$, and [Si$\,$]{} $\lambda 6355$ features have excitation energies of 6.9, 10.0, and 8.1 eV, respectively. Because the [Si$\,$]{} $\lambda
3858$ and [Si$\,$]{} $\lambda 5972$ features have very different excitation energies and [Si$\,$]{} $\lambda 6355$ has an excitation energy intermediate to the other two features, the strengths of the [Si$\,$]{} $\lambda 3858$ and [Si$\,$]{} $\lambda 5972$ features should change in opposite directions with changing temperature. This also explains the [SYNOW]{} results since [SYNOW]{} fixes the 