Fraction of random fields for which the corresponding detection statistic exceeds a given threshold. In each panel, the grey line shows the fraction for random positions. The red dashed line indicates the ACT DR5 candidate sample, while the blue dashed line corresponds to PSZ2. Left panel: Distribution of the zCluster density contrast statistic δ for random positions. We find that 5% of the random fields have δ > 3. Middle panel: Distribution of S/N values in yPlanck maps. We find that 5% of random positions have S/N > 1.7. Right panel: Distribution of S/N values in yACT+Planck maps. Selection threshold is S/N > 2. All catalogues are restricted to the ACT DR5 footprint.