That's not what radius means... radius basically means how much it will deviate on the way to its target, similar to the noise value. Noise, however, means how much tiny arcs and cracks the beam will make. A high radius would mean the beam makes big turns and arcs on the way to its target.
To achieve a sense of randomness, use several info_targets with the same name and the beam will strike a random one. Not tried this myself, but I think that's how it works, anyway.