Variation of the spectral shape with the steepness of the density profile n. We plot specific flux f_λ in arbitrary units for a sequence of emulated spectra where only the power law density index n is modified between spectra; the remaining parameters have been chosen to provide a good fit to SN 1999em for 9 November 1999 (see Fig. 8). We color code the plotted spectra by the power-law density index n.