Left: mass increase (kg m⁻¹) for the three simulations (viscous, solid lines; ideal, dashed lines; non-driven, dotted lines). The black lines correspond to the integrated mass in the coronal part of the domain whereas the green lines represent the mass in the non-coronal part. Right: mass increase (kg m⁻¹; blue lines) but now only integrated over the coronal part of the shell region (viscous, solid lines; ideal, dotted-dashed lines). The green lines represent the time integrated, averaged mass flux (where the averaging is done over the 4 boundaries of the shells).