Top panel: Temporal evolution of the azimuthally averaged gas surface density in the α = 10⁻⁴ model, with the Stokes drag region outlined by the black curves. Bottom panel: Radial profiles of maximal dust size (cyan line), fragmentation barrier (dashed red line), and maximum size of grown dust up to which dust dynamics can be described by the Epstein drag (dashed yellow line). The profiles are shown at a time instance of t = 500 kyr after the onset of simulations.