Histogram of the semi-major axis of particles with different radii, as indicated in the legend. The histograms are stacked in order of increasing size: the red histogram includes particles R_s = 1 mm, the green histogram includes particles R_s ≤ 1 cm, and the blue histogram includes all particles. All solids start from beyond 20 a, and only the larger particles drift towards the circumprimary disc. The results shown refer to the base model.