Case4 analysis. The left panel shows the characteristic strain spectrum compared to the f^−2/3 trend (dashed black line). The sensitivity curve is the one presented in The International Pulsar Timing Array Collaboration et al. (2023). Right panel: comparison between the recovered angular correlation in the residuals for this specific realisation (light blue points) and the results for the EPTA DR2new dataset (red). The expected variance of the optimal correlation estimator, for the EPTA 25 best pulsars array, is derived from prescriptions in Allen & Romano (2023).