Index δ of the power law modifying the starburst attenuation curve versus the V band attenuation for the clumpy ISM models of Seon & Draine (2016) with a Mach number of 4. Each colored line represents a model with a varying V-band optical depth and for a fixed distribution of stars and dust, parametrized by the ratio of their radii (Rs/Rd, for additional detail see Seon & Draine 2016). The solid lines represent a dust composition following the SMC dust model of Weingartner & Draine (2001) and the dashed lines that of Witt & Gordon (2000). The dash-dotted horizontal line indicates the slope of an SMC curve in the case of a pure screen geometry. We see that at fixed attenuation, the more extended the stellar distribution is compared to the dust, the flatter the attenuation curve is.