This is a behaviour I have noticed on several occasion with flies. When mating, the male seems to prefer to put his front pair of feet on the females compound eyes. Not really sure why, but perhaps it is a way to signal that she shouldn't fly away? If you do now, please leave a comment and make me smarter.
As for the species, I'm sorry to say that I am drawing a blank there as well. It's not that I can't find a robberfly that fits, but more a case of more than one species being a possibility. These two were getting busy on the side of my house as I was out with the wife in the garden and (sort of) helping her with it - bugs like these just need to be photographed, right?