Evolution of the S/N detection strength (measured at the position of the strongest peak; see Sect. 4) with increasing SYSREM iteration. We show the S/Ns of WASP-33b and KELT-20b in the left and right panels, respectively. The different Si abundances are indicated by different colors. The strongest S/N peaks are found for both planets at [Si/H] = 0 and are indicated by the blue stars.