Fraction of the domain volume occupied by the shocked ISM region up to a time t = 20 for different cases. This volume fraction of the shocked region both depends on the opening angle and on the density profile of the ISM. We know from Fig. 8 that all simulations have comparable radial reach, therefore we expect the volume of the cases to be ordered as in Fig. 9. This is the case within the same series of simulations (cases C, D and E, and cases F and H).