My experience (forms my opinion, so tkae it for that...) is the further back on the frame the bars terminate, the more structurally sound the cage will be in the event it's needed. In a rear impact, the bars' angles transfer the maximum amount of force to the main hoop and around the driver. The more sharp the angle, the less force will go to the hoop because the rear of the car will buckle. In terms of torsional (twist) strength, shortening the bars will reduce teh leverage teh cage has on the frame rails. The weight carrying spot is relocated by using the air bag crossmember. But the frame rails will still feel the twist from the floor and front rails. Take two pencils and a friend. Have him hold the point end with one in each hand, parrallel, and hold them about 2.5" apart. You take two fingers on each hand, and "pinch" each pencil between your finger at a point about 2" in front of the eraser end, and have him raise his right hand while you try to hold the pencils level. But witching to any point the air bags will move the center of gravity quite a bit towads the front of the car. The pencisl will pivot around the point your fingers are holding them, and they will twist. Now, use four fingers of each hand, one pair pinching the eraser end, the second pinching 2" ahead (where the first attempt was made). Now have him raise his right hand slightly. The pencils cant move very easilly without them both moving. That's what the cage does in a drag car, regardless of the rear weight carrying point.
