Dependence of the modulation potential on the heliospheric and LISM properties. Panel (a): Modulation potential as a function of modulation boundary, normalised to a nominal value of 500 MV for r_bo = 121 AU, for different assumptions of the radial dependence of the effective diffusion coefficient. Panel (b): Modulation potential as a function of interstellar neutral hydrogen density, calculated via Eq. (5), normalised to a nominal value of n_H = 0.2 particles cm⁻³ for present conditions, corresponding to r_bo = 121 AU, again for different assumptions as to the radial dependence of the effective diffusion coefficient. See text for details.