Comparison of results from four different flux emergence simulations. The top panels compare two simulations with different initial field strength, but the same overall flux: (a) 10.6 kG; (b) 21.2 kG. In both cases the bottom boundary condition after the flux emergence is an open boundary as described above. In panels (c) and (d) the initial field strength is 21.2 kG, but we used different bottom boundary conditions. In panel (c) we allow for horizontal flows, but no vertical flows in regions with more than 2.5 kG field strength; in panel (d) we continued the inflow in regions with more than 2.5 kG field strength. Except for panel (d), where we did not observe spot formation, results are comparable.