form is much less than that of the S=3 form. This suggests that the S=6 form would be difficult to detect in the W-band EPR experiment. More intriguingly as shown in Figure , even at a 70% contribution of the S=6, the S=3 form still dominates the spectral envelope with the S=6 form mainly contributing a distinctive shoulder at around 3500 -4000 mT to the overall spectral shape. It is clear from the spectra presented in Figure of Chrysina et al that a poorer fit between experimental and a simulated S=3 spectrum exists in this very region. Figure shows that inclusion of the S=6 form (70%) gives rise to a much improved fit to the experimental spectrum. Additional simulations varying the ratio of the two spin systems are presented in Figures S7 where we can estimate that an S=6 contribution of between 60-70% is optimal.