well right now you dont it auto selects whatever it feels is most important, alltho the system does calculate multiple target groups so maybe ill add an option to somehow choose between them
the reason behind 2 balls is that in order for the shield center not to affect everything in the scene with same collide it has to project the exact same negative attraction as well. The particles that are supposed to make up the shield dodge that negative attraction via no self collision + specific collideset (call it frequency if you want) which means great compatibility with random objects but no structure so the second ball is there to provide self collision. I think this solution is superior to a single ball particle because a single ball generator would also make the thing not usable in most scenes thus is worthless.
