Weak-lensing mass-observed richness relation measured for the clusters at redshift z = 0.22 run with both hydrocodes GadgetX in blue and GIZMO-SIMBA in red, respectively. The blue points are thus the same from Figure 7. The solid lines show the linear regression model results, with the shaded region indicating the 1σ uncertainty on the intercept and slope parameters. In each sub-figure – where we consider two different stellar mass cuts when computing λ_obs, the right sub-panel shows the PDF of the scatter of the observed richness (using a Gaussian KDE) with respect to the best-fit linear regression model; the shaded bands mark the corresponding 1σ deviation: σ_{log λ}.