Test of the f_select variable in the randomised algorithm, i.e. the fraction determining the number of draws each line must have to be included in the three percentile sub-masks. From top to bottom: Using the full mask, f_select =0.5 sub-mask, f_select=0.33, and f_select=0.25. All the f_select cases refer to the 1st percentile sub-mask, as the other percentiles show deteriorated but analogous features. In each panel the solid line indicates the sinusoidal fit at the period found in Sect. 2. We observe that f_select =0.33 is the best trade-off between number of lines included and achievable RV RMS.