N V/Si IV ratio (color scale) as a function of the ionization parameter and the H I column density in the cloud. The dashed green and dotted black lines represent the column densities of N V and Si IV scaled by the metallicity, i.e., log N(N V) − log Z/Z_⊙ and log N(Si IV) − log Z/Z_⊙. Crosses correspond to measurements in the individual components in our sample. Typical uncertainties on the observed column densities are about 0.2 dex. While these uncertainties are considered when inferring the U and N(H I) ranges, they are not represented here, to avoid overcrowding the figure.