Evan, it has always been my understanding that the reason for the pull or tuck in knife is because the influence of elevator trim. Now elevator trim could be needed for a few reasons including CG being off. A good example is the MK Aurora I recently started flying. Initially it was very nose heavy and pulled to the canopy. As I started shifting equipment and adding weight to the tail the up trim has been reduced as has the pull to the canopy in knife edge.