Comparison of peak surface brightnesses (top) and MSMF-based spectral indices (bottom) determined inside the mosaic (S_M, α_M) and individual pointings (S_P, α_P) as a function of distance from the pointing center for 106 bright, point-like sources (0.9 ≤ S_t/S_p ≤ 1.1, S/N > 200) observed in up to 11 neighboring pointings at varying distances from the pointing center (gray points). In both panels the large red points and their corresponding errors indicate median values and interquartile ranges inside 5 equally spaced distance bins. In the bottom panel a linear fit is performed on the median values to obtain the needed correction of the systematic trend across all distances (see text for details).