well that pose isn't really called the prima porta
it's called the adlocutio
I was giving an example of one of many poses that has an outstretched arm.
The Prima Porta has been seen on some Imperial coinage, so it's a good example of how coinage could give the impression of the Roman salute looking like the national socialist one.
And strictly speaking adlocutio isn't a pose, but the pose of the Prima Porta is supposed to represent August giving an adlocutio.
He's in a contraposto pose with an out-stretched arm. (hence the cupid-ridden dolphin at the foot acting as a counterweight).