Theoretical curves for ratios of [S II], [O I], and [O II]. Horizontal dashed lines show the average ratio values in the redshifted and blueshifted jet lobes (red and blue lines), corrected for A_V = 1 mag. The shaded regions show the minimum and maximum ratio values taking into account the uncertainty in flux calibration and allowing for a range of A_V from 0 to 2 mag. Vertical dotted lines show the estimated n_e in the redshifted and blueshifted lobes based on the BE method in Sect. 4.3.