Distribution of timescale ratios t_drift/t_grow and t_visc /t_grow. The plus symbols (“+”) represent simulations in which planetesimals form, while the cross symbols (“x”) indicate simulations with no planetesimal formation. Blue and orange markers show the Sobol-sampled simulations, while red and green markers represent a subset of 30 selected simulations from these Sobol-sampled simulations, with a reduced initial global dust-to-gas ratio (ϵ_init = 10^−2.25). The dashed gray line denotes the fitted boundary of the planetesimal-forming domain.