Solar corona magnetic field maps extracted from Wilcox Solar Observatory (WSO) at the mean epoch of 20 R_⊙ ingress and egress. The dark solid line represents the magnetic neutral line. The dashed red lines correspond to the belt of the slow-wind region. The two marked points give the projected locations of the ingress (▴) and egress (▾) minimal distances at 20 R_⊙. For the MGS 2002 solar conjunction, the hypothesis of a  ± 20° belt is not relevant (see Sect. 4.1.1).