Normalised scale height profiles of our sample galaxies for two-component molecular discs. The solid thin lines represent the scale height profiles normalised to 1 at 0.3r₂₅. The blue squares with error bars and the thick blue dashed line indicate the mean normalised scale heights and an exponential fit to it, respectively. The thick red dashed-dotted line shows an exponential fit to the normalised scale height profiles assuming single-component molecular discs in our sample galaxies. The respective scale lengths of the exponential fits are quoted in the top left of the figure. See the text for more details.