Model clouds formed by selecting all the models with T = 10 Κ and A_V = 11.5 mag from the output of the grid listed in Table 2 for Taurus. These models are used to illustrate the calculation of the parameter R (upper panels) and R^30% (bottom panels) (see Sect. 4 and Table 3). Upper panels: red and blue lines show the polygons obtained by connecting the extreme values of each [S/H] model cloud. The parameters R is then calculated as the ratio of the red and blue contours intersection area over the total area. Bottom panels: grey lines are iso-density contours corresponding to 30% the point density peak in each model cloud. We show in orange the intersection between the grey contours corresponding to the two values of [S/H]. The parameters R^30% is defined as the ratio of the intersection area (area enclosed within the orange contour) over the total area.