Scale height of the particle layer H_p (top panels) and maximum of the local particle density ρ_p (bottom panels) as a function of time for all our 2D models that trigger strong concentration of solids at high resolutions. Each column represents one set of dimensionless stopping time τ_s and solid abundance Z. The scale height H_p, particle density ρ_p, and time t are normalized by the vertical scale height of the gas H, the initial mid-plane gas density ρ₀, and the local orbital period P, respectively. The solid and dotted lines are for a computational domain of 0.2H × 0.2H and 0.4H × 0.4H, respectively, and the resolutions are differentiated by different colors.