Random Unit Vector in Cone favors center?

I’m trying to use this as a way to add randomness to AI shooting. The problem that I am seeing is that it seems to favor the center of the cone and despite have a quite large radius (in my opinion. 20 degrees) even when at the full distance with this large cone, the hits still seem to come quite often for the now small character in this cone 10,000 units out.

Has anyone else seen this, or is anyone else using this method for AI accuracy and have any suggestions?