Deviations Δ_λ(t) between pairs of SN Ia spectra from the four SN models (W7, N100, subCh, and merger) at rest frame t = 4.0 day after explosion. Each panel shows a pair of SN models specified on the top of the panel. The typical amplitude of deviations in the UV (for distinguishing progenitor scenarios) is ∼100%, which is about an order of magnitude higher than the deviations due to microlensing. Distortions due to microlensing therefore do not affect our ability to distinguish between the four SN explosion models for various progenitor scenarios.