I spotted these unfamiliar flies gathering along a sandy path, in the vicinity of ground-nesting crabronids and bees. When they landed, all would adopt this head-down, abdomen-up posture. I saw a couple of aerial encounters, which may have been male battles. I did not see any male-female pairings.
Having never noticed this species before, I decided to collect one for later study. Photo 3 shows the venation of that collected specimen.

~10mm long

see also
https://inaturalist.ala.org.au/observations/185648424