If you fly very close to the base of CAS, there's another consideration: wake vortex. Here in NL, the Amsterdam TMA starts at 1500', and is used to vector CAS around for Schiphol at 2000'. Wake vortices can drift down 700' to 1000' below the flight path. Here, the informal advice, when flying underneath the Amsterdam TMA, is to stay below 1300' to be safe.
Still, in aviation we're lucky that we can separate in the vertical, and we are (almost) never at the same altitude as the beacon itself. I have heard numerous stories about yachties who use buoys as their waypoints, put them in the GPS and then slave the GPS to the autopilot while they sip coffee in the cabin. Inevitably, the autopilot does exactly what the GPS tells it to do - sail directly into the buoy!