Elastic scattering cross section, σ_ni, implemented in the Bifrost code to calculate η_amb. The different lines correspond to H–p collisions including temperature dependency and charge exchange (solid red line), H–e (pink), He–p (yellow), He–He⁺ (blue), He–e (green), H₂–p (black), and H₂–e (gray). For comparison purposes, the constant σ_ni curve has been added, corresponding to H–p collisions frequently used in the literature (dashed red line).