Contrary to expectations, there was no maximum scan range beyond which the linear relationship between the J coupling constant and the squared orbital energy difference broke down. Rather, the fitting range was limited by either encountering irrelevant electronic structures, or by encountering regions in which 1h1p excitations became relevant that are not included in the model assumptions. The latter, in addition to further polarisation and dynamical correlation effects, also limited the use of NEVPT2 results that would normally be expected to be more robust and quantitatively meaningful. Future developments aiming to decompose the overall J coupling constant into ferromagnetic and antiferromagnetic contributions should therefore expand the fitting equation to incorporate these missing spin polarization and dynamic charge polarization effects.