Sunapha belongs to a set of four, with Anapha, Durudhara and Kemadruma, that between them exhaust the ways the Moon may be accompanied. The definitions all exclude the Sun, and usually the nodes Rahu and Ketu, and that exclusion is the most interesting thing about the group.
The Sun is left out because of its relationship to the Moon rather than because of any judgement on its nature. The Moon's phase is a function of its angular distance from the Sun, so a rule that counted the Sun as an accompanying planet would be measuring the lunar phase under another name, and the tradition already has a separate doctrine for that, in which the waxing Moon is treated as strong and the waning Moon as weak. Excluding the Sun keeps the two doctrines independent.
The nodes are excluded on a different ground. Rahu and Ketu are shadow points rather than bodies, they have no sign rulership of their own in the classical scheme, and their inclusion in yoga definitions is inconsistent across the sources.
Sunapha itself, a planet in the second house from the Moon, is read as self earned resources, the second house's signification transferred to a lunar reckoning. The atlas describes the method rather than endorsing it.