To change (increase) the ratio you need to either move the pushrod pocket closer to pivot point (center of the rocker shaft in this case) or lengthen the distance from the pivot to center of the valve. A longer arm on the valve side of the rocker would also require you to move the rocker shaft farther from the valve stem to keep the tip of the rocker centered on the valve stem). Pushrod length would change only if a change was needed to keep the new configuation rocker arm (different ratio in this case) sweeping accross the center of the valve stem as it moves up and down following the cam lobe. Hope that makes it a little clearer.