Density distribution P(z) obtainedfrom a vertically varying diffusivity. The diffusivity profile in terms of α_z is given by the red curve. The particle stopping time is τ_s = 10⁻² and is taken independent of z. The distributions obtained from integrating the stochastic equation of motions (Eq. (4); black histogram) and the strong coupling approximation (Eq. (10); gray histograms) are consistent. The dark blue curve gives the normal distribution, for the particle scaleheight evaluated in the midplane (i.e., Eq. (15) with α = 10⁻³). The light blue curves gives the gas distribution, scaled by a factor 0.1.