Flux-weighted mean radius of the BLR isovelocity slices as a function of the Doppler velocity in the line profile. The mean radius is computed for the 20 isovelocity slices of the KD and EW models, with an emissivity ε = ε₀ (r_in/r)³, and seen at an inclination of 34°. A more complete version can be found in Braibant et al. (2017). Using the half-radius instead of the mean radius does not change the velocity dependence.