The key to nailing your shock/spring setup is understanding what a four-bar suspension system does. As the car powers through the turns it rolls onto its right side. This drops the left side of the axle down (left). Because of the way the four-link system is mounted it causes the birdcage to rotate counter-clockwise. Because the shock is mounted behind the axle, this actually compresses the spring, and helps push the axle down faster so that the tire stays in contact with the track. The opposite happens on the right side of the car (right). Now as the car rolls over its moving the suspension up. The birdcage still indexes counter-clockwise (looking from outside the car toward the driveshaft), but now the shock is mounted in front of the axle. The end result is the same: power to the ground.