Comparison between the height-averaged opening angle evolution from the numerical simulations in Nagakura et al. 2014 (right-hand panel, adapted from their Fig. 3) and those predicted by our semi-analytical model (left-hand panel). Each line refers to a different initial configuration (see text). Stars and upward triangles in the left-hand panel mark t_bo and t_bo + t_delay (see Sect. 3), respectively. The evolution for configuration M-th45 is not shown in the original figure.