Magnetic frame, showing the variation in height across the visible emission region bounded by two vertical dashed lines in purple. The fiducial point is indicated by the vertical dashed line in green. The component regions are separated by the vertical dashed lines. The asymmetric coverage of ϕ_b about the fiducial plane is due the variation in the motion of the visible point from high to low as ϕ_b decreases. Two zones (brown and blue) representing the two carousels are shown as well. The traversal of the trajectory is toward more negative ϕ_b, cutting first the carousel at higher height (brown) and then the carousel at lower height (blue).