There are a couple of species in the Eirmocides genus that are very similar to your sighting when viewed from the underside. Given the location of sighting, the patch visible through the front wing and the dark spot on tornus of the hind wing I believe this is most likely a female E. absimilis (easily confirmed with an image of the upperside). Will leave this one as Eirmocides (genus) till hear Suzi's thoughts re same.