Comparison of the widths of normalised stacked spectra for a single-component and two-component molecular disc at different observing inclinations. The solid red lines indicate the stacked spectra for a single-component molecular disc, whereas the blue dashed lines show the same for a two-component disc. Different panels represent the effect of different assumed inclinations. The inclinations are quoted in the top left corners of the respective panels. The stacked spectra of a two-component molecular disc were found to produce a systematically higher width than that of a single-component disc. See the text for more details.