Line densities of high-ionisation lines. The left hand panels shows the C IV absorption line densities with W_r > 0.05 Å. The C IV line densities at the highest redshifts from the E-XQR-30 survey (D’Odorico et al. 2022) are illustrated for comparison. The same E-XQR-30 data set was analysed in Davies et al. (2023a) and has been corrected for incompleteness. The right hand panel shows Si IV absorption line densities. The Si IV line densities for systems with W_r > 0.03 Å from D’Odorico et al. (2022) are illustrated for comparison.