Maximum grain alignment fraction ƒ_max in the case of a normalisation to the Lenz’s ratio for p_V/E(B − V) = 13%.mag⁻¹ (black line and ±20% uncertainty as dashed lines). Model results are shown for the case of a universal alignment function for both grain populations (pink circles) and for different alignment functions for carbonaceous and silicate grains shown as yellow squares and green diamonds, respectively.