Individual profiles along the central axis of the structure. Top/bottom panel: He i/Ca ii H. The inner footpoint corresponds to the uppermost profile, the outer to the lowermost one. The solid vertical lines denote the rest wavelength of the respective line. The dashed vertical lines in the lower panel mark the used photospheric iron lines. The spatial separation between two subsequent profiles was 5′′. The profiles were offset in intensity from each other arbitrarily for better visibility.