An adjacent reflector returning 10db might not be seen if outside the same beam.
True enough. But for significant parts of HMS Victory to fall outside the beam, the beam would need to be impossibly tight, or very very near the target. Even a radar with a 1 degree angular beam spread (impossibly tight) would have a beamwidth more than 170 meters at only 10 kilometers distance. HMS Victory is only 69 meters long. So at any useful range, the entire ship would fall inside the beam and every metal bit and piece on the ship would provide a useful return.