I have javelin with the siege barrage node allocated.
I went to the arenas test dummy and attacked the ground, moving slowly back until i would not get a hit on the dummy for a full minute of attacks. moving a pixel back towards the dummy would eventually land a hit.
I then equipped an amulet with +40% area of effect, and attacked the same spot (that leads to no hits with no amulet) and attacked for about two minutes with no hit. Went one pixel closer, got a hit. I took the amulet off again to test the two locations, and it seems that +AoE does nothing for javelin.
I would have expected it to increase the area of the individual hits, and/or the radius at which projectiles fall from the center. It seemed to do neither as I would have expected to see a hit with either.
I can rerun the test and record if needed.