Polarisation spectrum observed by SOFIA/HAWC+ and JCMT/POL-2 (black dots) at 12 different locations in OMC-1 as shown in Fig. 2 with the best one-phase model. The reduced chi-square $\left({\chi }_{\text{red}}^2\right)$ indicates the ‘good goodness’ of the fit. The standard χ² is shown in Table 1. For comparison, we show the APEX/PolKA observations at 870 µm as a gray dot, but exclude them from the fitting. For visual guidance, we colour the frame blue for ${\chi }_{\text{red}}^2$, brown for ${\chi }_{\text{red}}^2$, and red for ${\chi }_{\text{red}}^2\ge 10$.