Left: the evolution of the maximal apparent velocity (β_{app, max}) as a function of the jet opening angle for the different velocity profiles D_{1 − 4}. Blue circles: profile D₁; violet triangles: profile D₂; green crosses: profile D₃; salmon crosses: profile D₄. For all profiles, we have set γ₀ = 10 (top) or γ₀ = 30 (bottom). Right: same as left, but for the Doppler factor.