4L of air in wings, versus 4 L of air around your body. Yeah, tested that too, but we forced the diver to go through the water at the same angle of attack for comarison. However, if wings are dragging 4L... they are bending the diver or tilting him. Air distributed around the torso keeps the attitude of the diver more consistent... and the numbers of actually testing the diver in true horizontal fashion is more correct. Hence, sure, the ADV type vests are less drag in this scenario, based on a few truisms/perceptions/observations/realities.