Average flux between 2R_200c and 3R_200c outside central clusters as a function of redshift, along with their 5σ significance thresholds (top panel). The result was obtained by removing all halos above 10^13.5 M_⊙/h. The bottom panel shows the required number of clusters to achieve a 5σ detection as a function of expansion factor, a. The corresponding redshift is indicated along the top. These results are based on eROSITA observational systematics and assume an exposure time of 100s.