ACT cluster masses $M_{500\mathrm{c}}^{\mathrm{UPP}}$ vs. the eROSITA fluxes in the 0.5−2.0 keV energy band for the subsample of ACT/MaDCoWS co-detections from Orlowski-Scherer et al. (2021). X-ray fluxes have been corrected for the expected bias arising from the different resolved fractions of compact sources in the cluster and background regions (see Appendix B). The best-fit relation (2) with η = 0.8 ± 0.03 is shown with a black line and gray shaded area. The dashed and dash-dotted lines illustrate η = 1 and 0.6, respectively. Cluster redshifts are shown with colors.