Presumably less energy is caught by somehow reducing pressure...

Presumably less energy is caught by somehow reducing pressure differential around the BA. (perhaps by opening it up - I have not read the patents). I suspect that with tweaking the components such as pumps, tethers and piles you could design a system which is more suitable for a higher mean wave height, possibly with a trade off of less power at lower heights and greater cost. I am sure that with the experience that CWE must have by now that they have run through many many variations.