comparing H. hydralis https://inaturalist.ala.org.au/observations?place_id=6744&preferred_place_id=6744&quality_grade=research&taxon_id=341542 & H. undalis https://inaturalist.ala.org.au/observations?place_id=6744&quality_grade=research&taxon_id=208101 the shape of the white line below the patch/reniform-ish mark seems to separate the sp. In H. undalis the line has a large, fairly smoothly curved dip below the mark with fairly straight line either side. In H. hydralis this line slopes down from the inner margin, about 2/3s across the wing below the patch it angles up for a bit then levels out across to the costa.