Same as Fig. 8, but for the reference model Ref-med. Settling is less efficient than in the standard model, and most of the dust grains remain near the upper surface of the disk. Regions just outward of the disk surface along the midplane show sufficiently high dust-to-gas ratios. These regions, however, do not survive to the last snapshot shown here. Planetesimal formation predominantly occurs along the midplane, highlighted by the grey arrow in the forth panel, and shown below.