Common sense tells me that the spine should be in line with the flexing force of the cast. Clearly when the force from the casting hand is applied directly in line it makes a difference, therefore it only makes sense that the flexing characteristics of the rod should also be in line with the plane of the cast.
If a rod was held sideways in the hand and cast with a 'wiping' motion I think all would agree that much is lost vs. direct alignment with the thumb or palm. Therefore if the rod's spine is askew to the plane where force is applied, I would think there is a direct analogy in terms of physical characteristics to the 'wipe'.
With a single hander, pushing the thumb toward the target means pushing the blank directly in-line. I prefer a vee-grip with a Spey cast for the very same reason.
Nobuo insists on spine alignment with the casting plane for CND rods. For me it's just common sense and gut feel, but he must have a real reason.
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