The Hatha Yoga Pradipika describes virasana in a single verse: one foot placed on the opposite thigh, the other tucked beneath the opposite thigh. Svatmarama makes no promise about it and attaches no benefit. It is presented as a way of sitting and nothing more.
Vira means hero, man, or one possessed of strength, and it is a word with a substantial afterlife in the tantric literature, where vira names a particular kind of practitioner and a corresponding mode of practice. The hatha manuals do not draw on that sense here, and the atlas does not attach it to the posture; the entry is bare and the atlas keeps it bare.
Both surviving manuals carry the posture, which places it among the shared stock. Within the Pradipika's fifteen it belongs to the asymmetric seats, where one leg is arranged differently from the other, alongside gomukhasana and the twist named for Matsyendranath. That subgroup is small and it is one of the places where the earlier manual is more varied than a summary description of it as a book of cross legged seats would suggest. The corpus offered a practitioner a real range of ways to arrange the legs for long sitting, and left the choice open.
An entry given without a claim also tells a reader something about how the Pradipika's fifteen were meant to be used. The four postures Svatmarama singles out carry promises; several of the remaining eleven, this one among them, carry none. What the text is offering is a set of workable seats with a small number elevated above the rest, not a graded programme in which every item has an assigned outcome, and the bare entries are where that structure is easiest to see.