Schema of an MC cross-section used to define the MC parameters defined by Démoulin et al. (2019). The MC interval, deduced from in situ observations, is schematised with a thick green line. The dashed circles represent the boundary for three characteristic FRs: in blue for the in situ FR, in black for the fitted Lundquist FR limited within B_z(R₀)=0, and in red for the expected fully formed FR without erosion at its boundary. Two cases are shown: (a) R_in >  R₀ >  R_out and (b) R_in <  R₀ <  R_out corresponding to the MC examples shown in Fig. 4.