: Ideally water doesn't flow past the paddle, it grips the water
: without letting water past.

Water ALWAYS flows over the blade, there is no way to prevent that. You don't want to prevent it anyway, as flow across the blade when using a canted stroke produces a degree of lift and more bite. The smoother the contour, the better the flow and the more efficient the paddle.

The shape in the Gail Ferris diagram above is excellent, though if you make it with more pronounced shoulders, the shape will start out as more of a rounded diamond at the shoulders, transitioning to the lenticular shape at the ends.