X-ray ionization rate in the midplane (left panel) and for a vertical cut at r = 150 au (right panel) for models with fixed stellar X-ray luminosity (L_X = 10³⁰ erg s^-1) but varying X-ray background fields with fluxes of 2 × 10^-4 (blue), 2 × 10^-5 (brown) and 2 × 10^-4 erg cm^-2 s^-1 (red); the black lines are for the model without an XBGF. The solid lines are for the full X-ray spectra (0.1−20 keV); the dotted and dashed lines correspond to models with a low-energy cut-off at 0.3 keV and 1 keV, respectively. The horizontal lines mark the cosmic-ray ionization rates for the ISM (ζ_CR ≈ 10^-17), and low cosmic-ray case (ζ_CR ≈ 10^-19 s^-1). In the right panel, the vertical grey solid line indicates the scattering surface at N_{⟨ H ⟩ ,rad} = 2 × 10²⁴ cm^-2 (see also Fig. 7).