Notes. The columns, from left to right, indicate the inversion test number, the spectral lines included in the inversions (where “blends” refer to those in the Mg I b₂ line listed in Table 2; smaller or unknown blends in the Mg line were masked in all tests), the spectral window of the inverted FTS atlas profiles, the wavelength sampling of the FTS profiles, the atomic model used for the Mg atom, the inclusion of opacity fudge (OF), and the NLTE threshold used in each of the eight inversion cycles. In test 8, the spectral window and wavelength sampling refer to those of the inversion grid only, since the FTS profiles were inverted using only the wavelength points that coincide with those of our SST observations as detailed in Table 1, i.e., using 14 wavelength points in the Mg line and 18 in the Fe line; see Fig. 3.