MOLPOP-CEP non-LTE radiative transfer modelling results for the W51E cloud components at υ_LSR = 65 km s⁻¹ (top) and 67 km s⁻¹ (bottom), respectively. The red contours display the 1, 2, and 3 σ levels of the χ² distributions of the modelled line ratios that best reproduce the observed line ratios between the 3.264 and 3.349 GHz lines (R₁) and those between the 3.335 and 3.349 GHz lines (R₂) across the n_H2−T_kin parameter space probed for the CH column densities and line widths specified above. The dashed red lines mark the minimised values and 1σ limits.