Dependence of η_Crit on the overdensity, χ. Red dots show the numerical results. The blue line shows the theoretical expectation assuming that only the low density is relevant for kinematic viscosity. The red line shows that only the high density is relevant. The green line assumes an arithmetic mean of kinematic viscosity between the fluids. The black line shows a harmonic (weighted) mean. Note that we normalized the values of viscosity to the Spitzer value at 10⁶ K.