This has been a very active question as of late. This exercise seems to be very individual, and different folks seem to have different strokes. The main thing is to find a comfortable grip, and have a smooth pressing motion.
With both myself and my athletes, I use a grip no wider then 12-14 inches. I prefer to use a true grip (thumbs grasping the bar) and a slow concentric movement. Elbow posisition is not really a factor, so long as the arm is extending, the tricep is woking. Just play around w. the techniques till you find something you like, and go with it. Good luck.
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