ΔV as a function of average magnetic flux for the structure approach at disc centre (μ > 0.95) vs size for different ranges of B (upper panel) and vs B for different ranges of size (lower panel), for Set 1 (dashed) and Set 2 (solid). The black curves are for all B (all sizes). The vertical black lines correspond to the typical granular size (dashed), the box size (solid), and the 20 ppm scale (network-active region interface, dotted).