Left column: In-plane distribution of the electric current density (color-coded) and magnetic field (blue stream lines) in selected FPIL-normal planes. Closed black contours mark the regions with the strongest electric current (95th percentile of the current density in plane), used to locate the current-weighted center of MFR (SA) (black cross). The vertical dotted red line marks the location of the FPIL. Vertical orange lines mark the extent within the FPIL-normal plane within which the decay index was analyzed. Blue (red) contours indicate where n exceeds 1.5 (0.8). Middle column: Decay index on selected FPIL-normal planes covering the FOV indicated by vertical orange lines in the respective panels of the left column. The dotted gray line and shaded region indicates ${\overline{h}}_{\mathrm{crit}}$ (using n_crit = 1.5 and n_crit = 0.8) and the corresponding spread when averaged over all considered FPIL-normal planes. The layout is the same as in the left column of Fig. A.2. Right column: $\overline{n}$ vs. height profiles derived from all of the FPIL-normal planes (their footprints are indicated in the respective panels of Fig. A.1). The layout is the same as in the right column of Fig. A.2.