The ability to adjust the lateral position of the frame both under the heel and under the ball of the foot gives a lot of room for customization. According to Nick, the frame should center under the heel for maximum force transfer through the heel in the pushing phase of the classic stroke, and should angle inwards through the ball of the foot. I have also heard that the frame should be positioned such that the distributed center of weight across the foot is directly over the line of the frame when the skater is in a neutral glide position. In this way the skater does not need to expend energy to keep their foot on top of the frame in a glide allowing a glide with minimal effort. Since the classic technique is one half push with the heel, and one half glide with the other skate, this type of frame positioning makes sense. I don't know whether the double-push could benefit from an altered frame position.