Expected (red line and region) and observed (black dots) number of RHs in PSZ2 clusters with a flux density greater than f₁₅₀ and within z ≤ 0.5 in the LoTSS-DR2 area. The black arrow shows the upper boundary to the total number of RHs (due to classification uncertainty), and the bars on the black dots are obtained by a Monte Carlo procedure and represent the errors due to the uncertainties on the flux densities of RHs.