koobas.hobune.stream
Particle System Collision Mode
Is there any chance to get in the World mode the "Particle Radius" parameter from the Plane mode? 
Can you try accessing the Particle System component through the GetComponent method? Mostly after accessing the Particle System component, you may have an option to get the Particle Radius parameter. As far as I know, those sub-menus of Particle System can be accessed by this method.
