Open water is a bit of a misnomer as it implies somewhere away from the shore out in the ocean. It's probably more difficult to go faster on a man made location like Luderitz where the chop is quite nasty due to the constraint and reflection off the leeward bank. Behind a sandbar tends to be flatter as the chop/waves disperse downwind. Adding all these descriptions and names for separate records tends to dilute the whole idea of a record in the first place i.e. the fastest period! Leave it as it is. Additionally what allowance is made for the current that exists in tidal locations like the Brace, it's measured in man made spots like Luderitz I believe.
Roo, I prefer it au natural with speed chat