Optical dust attenuation slope across the Balmer break (A₃₅₀₀/A_V) vs. the optical attenuation A_V. Radiative transfer models predict a strong correlation between the slope and optical depth (Chevallard et al. 2013), which closely matches observed dust curves (Gordon et al. 2003, 2009; Salim et al. 2018). The various black symbols denote optical slopes and depths implied by the SED models of The Cliff from Section 5 (medians are shown with 16–84 percentiles, although these error bars are in most cases smaller than the markers), which deviate strongly from this trend. The dust-reddened BH* model is discussed in Section 6.4.