Predicted column density of N V, Si IV, and C IV (top) and the N V-to-Si IV and N V-to-C IV ratios (bottom) as a function of the ionization parameter. The solid lines correspond to the log N(H I) = 15 model in Fig. 3. The dashed (dashed-dotted) lines correspond to models that assume a ten-times-higher (lower) metallicity. The shaded areas show results from the central model (solid line), simply scaled up and down a posteriori by 1 dex. These scaled results match the predictions from the full calculations with corresponding metallicities reasonably well, typically within a factor of two (illustrated by the width of the stripes).