Same line ratios as in Fig. 3, but for smaller CLOUDY grids varying the ionization parameter and the density of the cloud to test stellar populations (a single 2 Myr population in the top left, 7 Myr in the top right, and 20 Myr in the bottom left) as a source of radiation, instead of an AGN. In the bottom right we test a constant pressure density profile instead of the constant density one.