S/N maps of WASP-33b after three SYSREM iterations from model spectra with non-solar Si abundances. The top panels and bottom panels correspond to sub-solar and super-solar [Si/H] ratios, respectively. The yellow dashed-dotted lines indicate the location of the most significant detection peak, described in Sect. 4. The detection significance obtained with non-solar [Si/H] ratios is below the peak value obtained under the assumption of solar elemental abundances.