Rosseland mean opacities κ_ross as a functionof orbital distance in our disc model using α = 0.001 and u_f = 1 m s⁻¹ for all chemical compositions. We vary the chemical composition of the grains in the disc following the approach of Bitsch & Battistini (2020). Here, [Fe/H] implies only a change of the composition of the grains (Table 2), not a change of the dust-to-gas ratio. We note that in Bitsch & Battistini (2020), [Fe/H] = 0.4 implies a very low water fraction, while [Fe/H] = −0.4 provides a large water fraction.