Inverse of the HCN emissivity (in units of the HCN conversion factor) as a function of HCN intensity. We plot the PHANGS-, NGC 4038/9-, and NGC 3256-type models from left to right as the blue, orange, and green filled contours. The black contours represent ⟨ϵ_HCN⟩⁻¹ for the models where we make a cut at 0.1 K km s⁻¹, which is analogous to a sensitivity limit in observations. For comparison, we also show the Gao & Solomon (2004a,b) value as the black, dotted horizontal line and several published values of α_HCN from observations of Milky Way clouds (Dame & Lada 2023; Shimajiri et al. 2017). The gray, filled contour represents all models. We find the HCN emissivities from the PHANGS-type models to be most strongly impacted by a sensitivity cut. These models appear to have artificially lower ⟨ϵ_HCN⟩⁻¹ (higher emissivity) as a result of the cut.