Results of the optimal sub-bin combination search with four sub-bins. Top panel: optimal configuration of four 10 Å bins as a function of wavelength for the FALC atmosphere model. The color-coding shows how sub-bins are distributed relative to the bin length (see text for details). Middle panel: ratio of ODF to detailed spectra using the best combination of sub-bins for each bin from the upper panel (blue). For comparison we also show accuracy using Kurucz sub-bins (orange). Bottom panel: ratio of ODF to detailed spectra using the best sub-bins for each bin from the upper panel applied to the FALP atmosphere model (blue) and using Kurucz sub-bins on the FALP atmosphere model (orange). The values of the ratio in the middle and bottom panels greater than one were mirrored over the abscissa y = 1.