Normalized electron heat flux as a function of a measure of collisionality. Top panels: 2-d frequency distributions of heat flux and the Knudsen number K (the ratio between the mean free path λ_fp and the temperature gradient scale L_T) for two values of the electron temperature exponent α (i.e. T_e ~ T₀r^−α), for the first two PSP orbits (heliocentric distances <0.25 AU). Bottom panels: same quantities for the fourth and fifth orbits. Frequency values are column-normalized to a maximum of unity for each value of K, with the same color scale as Bale et al. (2013) for ease of comparison. Diagonal lines mark a 1:1 relationship.