Circular polarisation fraction as a function of θ for different T_BΔΩ, for 6.2, 6.7, 25 and 45 GHz methanol maser baselines. Magnetic field strength is 10 mG, thermal velocity width is 1 km s⁻¹. For the 6.2 GHz methanol maser, the T_BΔΩ corresponding to the gΩ = 10R limit is ~ 2 × 10¹⁰ K sr; for the 6.7 GHz methanol maser T_BΔΩ corresponding to gΩ = 10R is ~ 10¹⁰ K sr; for the 25 GHz methanol maser T_BΔΩ corresponding to gΩ = 10R is ~ 10⁹ K sr; for the 45 GHz methanol maser, the T_BΔΩ corresponding to gΩ = 10R is ~ 9 × 10⁸ K sr.