Total CR energy in the box the different runs of the G9 galaxy. The higher the diffusion coefficient, the higher the CR energy: the reason is that the more CRs can diffuse, the more they can escape high gas density and CR-energy-density regions where the CR cooling rate is higher. At the beginning of the simulation, with isotropic diffusion, CR energy quickly escapes in directions perpendicular to the disc, whereas it remains trapped in the disc for anisotropic diffusion.