Distribution of z-scores for simulations performed for a variety of 21 cm signal shapes. The two columns show the results for standard and cross-GPR. The top panel shows the dependence of the z-score on k, for the different nights. The gray bands indicate the 1σ and 2σ levels. The bottom panel shows the dependence of the mean z-score on the 21 cm signal shape. The normalised power spectra for the different signal shapes are shown with colors indicating the mean z-score. The shape of the excess component power spectrum is indicated in each panel with dashed black lines.