Example forward model calculations showing how the force balance at the bottom of the domain is insensitive to A) the melt viscosity as \(\eta_{f}\rightarrow 0\) in the limit that \(\delta_{c}\gg H\left(t\right)\) and B) the effective matrix viscosity as \(\xi_{\text{ref}}\rightarrow 0\) in the limit that \(\delta_{c}\ll H\left(t\right)\).