Mean detection significance of proto-clusters as a function of aperture radius (top) and as a function of the completeness limit (bottom). The set-up is similar to Fig. 13, but with a local background and an aperture radius in arcminutes. Top: A redshift interval of Δ_{z (50%)} was used. Bottom: Values of the completeness limit, Δz (X%), in the range of 30–90% were used. The solid lines show the results for an aperture radius of 0.5 r_pc and the dashed lines show the results for 1 r_pc.