The cushion plunger is used for adjusting center shot and offsetting shaft resilience. It does not change the spine (stiffness) of the arrow. The arrows spine is what it is. It does not change. A specific shaft will bend "X" ammount with a specific ammount of weight attached. The cushion plunger simply helps the arrow stay straight when traveling down the sight window.
I bend the inner side up to make a side wall for the arrow to ride along.
I bet you dollars to donuts that if you recorded it with a slow motion video the prong you bent up is completely out of the way in the first six inches or so and actually does nothing to "cushion" the arrow as it travels down the bow.