Distance–mass diagrams for single-embryo populations with varying parameterisations of Σ_active. Top row shows results for temporally and spatially constant Σ_active, while the bottom row shows results with the accretion velocity being a fraction of the local sound speed, f_s × c_s. Accretion layer thicknesses increase from left to right. Formation tracks are shown for 200 randomly selected simulations coloured by migration regime.