As the sun rises from 15° to 27°, the supralateral arc almost overlaps the upper half of the 46° halo, which is why many reported observations of the latter most likely are observations of the former.
When the sun begins its ascent from 15° to 27°, the supralateral arc encroaches upon the upper portion of the 46° halo, leading many observers to mistakenly record sightings of the halo when they actually observed the supralateral arc.