That is basically true. A longer fetch from a storm in the north Atlantic results in a longer wave length swell near the BVI. Longer wave length also means deeper effect. If you are in deep enough water that the wave can't feel the bottom it can be comfortable. As the wave reachges shallower water and feels bottom it starts to slow down and wave length shortens. That enegy has to go somewhere so it goes up and gets nasty.

Cooper is an interesting case. Cistern Point pretty well protects it from anything from the east but from the north it gets hit by both the source swell and reflections off Salt. BUT there is also a trade wind effect to be aware of. Even in the best of conditions updraft of the heat from the island's surface keeps the trades high during the day. As the land cools at night the trades descend and are squeezed through the gap at Haulover Bay. Cistern Rock turns this flow into a train of vortices that roll over the anchorage and, with the lack of current, wind controls a boat's orientation. One minute a boat might be bow on to the swell and the next broadside.