Calibration curve of Hanasoge et al. (2012, Fig. 2 in the supplementary material) can be reproduced (blue solid curve). When a more realistic width σ_z′ = 16.8 Mm = 1.8 H_P of flow features is used to compute the calibration curve, a change is seen (dashed orange curve), which would lead to an increase in the estimated upper limit, see assumption (A6). The crosses and pluses indicate the grid points in harmonic degree, which were obtained by converting horizontal Fourier modes from Cartesian to spherical geometry (see Appendix A.4). The kernels and thus the calibration curves shown here were computed on a spatial grid with a four times larger spatial extent than the MURaM grid, therefore the resolution in Fourier space, , is four times finer than in other plots in this paper. See Fig. C.2 for a more detailed comparison.