Alan, as I understand it, the lateral area of any fin keel is pretty much insignificant for resisting lateral slippage unless you're making little or no forward way. They all work by generating lift as the boat moves through the water. And a high-aspect keel as in your picture will produce more lift per unit of lateral area because more of the area is far from the tip, where you get pressure bleed-off as water moves from the high pressure side to low pressure. Of course, having a bulb on the tip further reduces this migration.