Collisional mean-free paths as functions of height. We show the mean-free paths between ions and neutrals (λ_in, red lines) and between neutrals and ions (λ_ni, blue lines) for the two collisionality regimes considered: self-consistent from plasma-neutral parameters (2fl, solid lines, left axis) and reduced-case 2flα (dashed and dotted lines, right axis, with a different order of magnitude). The collisional mean-free paths were calculated according to Eq. (8).