Correlation between the local dust-to-gas ratio ϵ and the deviations in the velocity of the gas u_z (full line) and particles v_z (dotted line). To aid interpretation, we subtracted the mean velocity of the sedimenting particles ⟨v_z⟩ from the particle velocity and a small artificial upwards mean gas velocity ⟨u_z⟩ from the gas velocity. Displayed are different times t = 0,5,10 t_f, in respectively black, blue, and red, based on the region between z = 0–10 l_f in run2. The standard deviations on the binned averages are relatively large, σ ≈ 0.03–0.04 v_f for the gas and particle velocities between t = 5–10 t_f. The black dashed line corresponds to α = 0.02 in the toy model (Sect. 3.5).