The downstream male. I didn't get a good angle (he caught on to my edging around before I could get the lateral view I wanted), but I can't see how this abdomen tip could correspond to the abdomen of P. hinei. Are there good closeup illustrations somewhere?
One of four large robber flies working the gravel bar: two were clearly female Proctacanthus rufus/hinei, and I thought the other two, including this one, were likely male P. rufus. But the AI's top choice for this one is Promachus hinei, followed by Proctacanthus hinei. So it seems to be a matter of one step forward, two steps back in my efforts to understand just a little about robber flies.
The light is terrible for this one. I'm hoping I got better images of the second male.