Mass M_2−2.5 of the shell with radii 2R₂₀₀ and 2.5R₂₀₀ as a function of M₂₀₀. The colour code shows the dependence on redshift. Circles, squares and triangles refer to the CIRS, low- and high-mass HeCS sample, respectively. The open circles show the median M_2−2.5 of the N-body clusters of our two simulated samples, estimated from their three-dimensional mass profiles. The crosses show the median M_2−2.5 obtained from the NFW fits to the three-dimensional mass profiles: on average, they overestimate the individual true mass of the shell by ∼22−28%, depending on the mass bin.