Unit vectors K (arrows) giving the direction of wavevectors k of large-scale structures, at z = z_h, projected on the horizontal xy plane. The starting points of each unit vector (large square dots) are the (x,y) positions of the corresponding rays at z = z_h. The dotted area represents the area at the base z = 0 where B_z ≥ 0. The segment AB is also plotted.