Maximum distance from the jet origin at which a given fraction of momentum flux is carried by material moving at γ ≥ 5 as a function of time. The four panels refer to the four different cases (Case A: top left; Case B: top right; Case C; bottom left; Case D: bottom right). In each panel the top curve shows the jet head position and the other curves represent the fractions from 10% to 70%. For Cases A and C we highlight the areas between subsequent curves with different colors.