Do you have a reference?
ICAO Annex 10 Volume IV is a good place to start. Surveillance and Collision Avoidance Systems Standards and Recommended Practices. My italic bolding added.
4.3.2.1.3.2
RECOMMENDATION
The errors in the relative bearings of the estimated positions of intruders should not exceed 10 degrees rms.
Note: This accuracy in the relative bearings of intruders is practicable and sufficient as an aid to the visual acquisition of potential threats. In addition, such relative bearing information has been found useful in threat detection, where it can indicate an intruder is a threat. However, this accuracy is not sufficient as a basis for horizontal resolution advisories, nor is it sufficient for reliable predictions of horizontal miss distances.