Magnetic field response functions, RF_B, of the Fe i 6301.5 Å  and Fe i 6302.5 Å  lines. Panels b) and c) show RF_B for Stokes I and Stokes V, respectively, for a penumbral atmosphere with the magnetic field strength stratification presented in panel a). Panels e) and f) are the same as panels b) and c) but correspond to the magnetic field stratification displayed in panel d). The presented RF_B values are normalized to the maximum value. The absolute values of RF_B, integrated over wavelength (Δλ = ± 0.35Å ) for the Fe i 6302.5 Å  line, are shown in panel g). Red and blue curves correspond to the positive and negative (ΔB/ Δlog τ), respectively. Solid curves are for Stokes I and dashed curves are for Stokes V. Dotted horizontal lines in panels b); c); e); and f) and dotted vertical lines in panel g) indicate the log τ nodes used in the inversions.