Results of a chi-square (χ²) test for finding the best match between the distributions of the diffusion index from observations and Monte Carlo simulations of the MBPs located in a supergranule’s bulk. The contours guide the eye to the best χ² value, giving the appropriate coherence time Δt for the random velocity and the ratio of random-to-systematic velocities v_r/v_s of the MBPs under study.