Histogram showing the total amount of mass in planetesimals that have formed at different locations in the disc after 300 kyr, for the nominal model and the midplane model. The amount of planetesimals formed around the gap edges of the two outermost planets are similar in both models; however, this is not the case at the innermost planetary gap edge. The settling toward the midplane is not efficient enough to counteract the stirring by turbulence in this region, and thus a dust-to-gas density ratio of unity in the midplane is never reached.