Most BVI overnight moorings state that they are good for vessels up to 60 feet. To me that implies that the seabed parts of the moorings are at least 120 feet apart. (I am simplifying somewhat and it's actually even greater that 120 feet.)

That is not true!

When they say good up to 60 feet they are only talking about the mooring's ability to hold the boat in place (and I believe that their receipt even has an upper end for wind speed, maybe 45kts). When the wind goes slack and currents get funky, boats start to swing differently, and can indeed touch in some locations.