Inputs of our preferred model. Shown in the panels are the H₂ gas density (top left), infall velocity (negative represents expansion; top right), ²⁸SiO abundance (middle left), H₂O abundance (middle right), and the kinetic temperature (in black) and excitation temperatures (in colours) of the three ²⁸SiO transitions (bottom left) and the H₂O transition (bottom right). In the bottom right panel, the solid red line indicates positive excitation temperature (i.e. non-maser emission) of the H₂O transition, and the dashed red line indicates the absolute values of the negative excitation temperature (i.e. population inversion) between 1.7 × 10¹⁴ and 2.4 × 10¹⁴ cm. Small negative values for the excitation temperature would give strong maser emission. Vertical dotted lines indicate the radii where the spectra were extracted; coloured horizontal dotted lines in the bottom panels indicates the upper-state energy (E_up/k) of the respective transitions. The innermost layer within R_continuum represents the grid cells for the pseudo-continuum, whose input values for H₂ gas density and molecular abundances are above the range of the plots.