Radial column density profiles for HCO⁺ and N₂H⁺ with (coloured lines) and without (black lines) XBGF for the ISM (top row) and low (bottom row) cosmic-ray case. The dashed lines are for models with a low-energy cut-off of the X-ray spectra (stellar and XBGF) of 1 keV; for the solid lines the lowest X-ray energy is 0.1 keV. The grey shaded area marks a factor of three difference in N with respect to the models without XBGF (the solid black line).