Dependence of the convective velocity u_conv on the boost factor b. The right vertical axis shows the corresponding Mach numbers computed using the reference sound speed c_ref = 7.96 × 10⁷ cm s⁻¹. Statistical-variation ranges for the individual data points are smaller than the markers and not shown. A straight line is fitted to the 2.5D data points using the Monte-Carlo procedure described in Sect. 3.2. The grey shading shows the 3σ statistical-variation interval around the mean fit. Parameters of the scaling law are given in the legend. The usual adiabatic scaling u_conv ∝ b^1/3 is also shown for comparison.