Line-of-sight velocity on-axis (at δx = 0) of the model disk-wind flow surfaces as a function of their poloidal velocity. Orange circles show the front side (), and green circles show the back side () of the disk-wind flow surfaces. In gray, we show the line-of-sight velocity range where the arches and cusps are observed (see Appendix B). In light gray, is represented the low S/N domain where the cusps could not be characterized.