Depth dependence of amplification factors (left column) and (right column) of Fe ii, χ = 6 eV, at λ   850 (solid) and 1600 nm (dashed) for the three red giant models of Table B.1 (top to bottom). The weighting function ℬ_2,2,2 for both wavelengths is also shown (solid blue and dashed red lines). Filled circles are centered at ⟨ T ⟩ _line and indicate the resulting effective amplification factors log ℛ_2,3,2 (left panels) and log ℛ_2,3,3 (right panels). Star symbols indicate the values of log ℛ_3,3,3 (right panels).