Relation between the peak optical depth of the 3.0 μm ice feature (${\tau }_{3.0}^{max}$) and the ice color excess Λ(W₁ − I₁) for different assumptions about the extinction law. The fitted curves correspond to extinction laws from Weingartner & Draine (2001) (blue), Draine (2003) (red), and Boogert et al. (2011) (black). While the use of the Λ(W₁ − I₁) metric minimizes the impact of extinction law uncertainties, systematic differences between the fits remain visible. However, these differences are generally within the typical measurement uncertainties of the calibration. This highlights the importance of adopting a consistent extinction law or recalibrating the method when applying it to different environments.