Different chosen paths (in purple) for the flux rope insertion method. The black and white color scale represents the modeled current density distribution. Left: path was aligned with the filament underlying the sigmoid, as seen in the 131 Å filter (Fig. 1a). Middle: circular path extending the filament, corresponding to a flux rope with a variable axial flux, as represented by the blue insert on the left of the sigmoid. Right: best-fit model corresponding to a flux rope with a constant axial flux, referred to as model S.