A friend of mine just realized something:
R3-A2 reads: "When you declare the target of your attack, if the defender is inside your firing arc, you may receive 1 stress token to cause the defender to receive 1 stress token".
According to the Attack Timing Chart, the attacked ship doesn't become the defender until step 1.v. That was the whole point after R4 Agromech's nerf.
Since the target is declared at 1.iii, that is the step where R3-A2 triggers (as happen with Rebel Captive). At that point there is no "defender" that can receive any stress token.
I think he's right, and that it's pretty clear that, RAW, R3-A2 is useless right now.