Lines of constant intensity ratio of C¹⁸O 5–4/7–6 (solid lines) and HCO⁺ 4–3/7–6 (dashed lines), resulting from a radex grid calculation. Curves are labeled by their line ratio value. The gray areas mark the 1-σ uncertainty ranges of the observed line intensity ratios in the outflow component, including the fit error (see Table 2) and the 10% calibration uncertainty (see Sect. 2.1). The darker gray area denotes the region where the observed line intensity ratios of both tracers overlap.