Comparison of the variation of the small-to-large grain mass ratio (D_S/D_L) with metallicity (left) and galactocentric radius (right) for M 101 (top panels), NGC 628 (middle panels), and M 33 (bottom panels) with the SPH simulations of an isolated galaxy performed by Aoyama et al. (2017) and Hou et al. (2017). Thick lines represent mean values for each model and the coloured areas cover the 25 and 75 percentile of the particle distribution. A solar metallicity of Z_⊙ = 0.02 was adopted.