Examples of ellipse fit for the structures of family B in two PV_⊥ diagrams formed at offsets of 6 and 8 arcseconds from the source. Feature B1 visible at 6″turns out to be composed of two concatenated substructures (B1a, B1b). In the PV_⊥ at 8″only feature B2 is clearly identified. Details of the fitting procedure are described in Appendix B. The small magenta ellipse indicates the instrumental uncertainty. The bottom right panel illustrates the identification of the coordinates of the apexes (x₋, V₋), (x₊, V₊) reported in Table 1.