I think I was suggesting the lettuce edge because the piping has a kind of ruffling to it, rather than being as big as the arm (this picture
shows what it would look like if it were only as big as the arm).
Your reference pictures look like there is more fabric/piping there than the circumference of the arm, so the circle shape buckles up and down like what I'd call a lettuce edge (top reference picture, raised arm shows it best).
Since your fabric is not stretchy, I'd make the arms larger than the circumference of the arm, and then sew the top to a ring of elastic streched out when making the piping. That way, there's blousing below the piping, and the piping has to collapse in what I call the lettuce edge.
Am I explaining that clearly?