Interesting question TJ. I guess for the most part, I grip the rod in the middle out of habit and because I thought it was the "sweet spot" on most rods. However, moving the grip down doesn't really make the rod any tip heavier or anything. I can see what you're saying about freeing up the wrist but I don't really feel gripping the rod in the middle is restricting my movement in any way and it seems to be comfortable for me. I notice Daniel and some other masters tend to grip the rod toward the bottom though. I'd be curious to see what others have to say.
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My blog: Tenkara TalkTenkara USA Rods: Amago, Ayu, Ayu Series II, Ebisu, Ito, Iwana 11', Iwana 12', Yamame
Other Tenkara USA Gear: Tamo, Strap Pack, 3.5 & 4.5 Level Line, 10.5 ft. & 13 ft. Traditional Line, Line Spools