Check the Convex hull of your PhysX shape to ensure it's big enough to encapsulate the particles.
If you're asking how to ensure they are separate at frame 0, and not simply during the sim later on, use a Particle Physics operator (with integration turned off, affect position on, and timing to entry) to separate born particles. Put it immediately after your Position Icon operator.
If you're asking how to ensure they are separate at frame 0, and not simply during the sim later on, use a Particle Physics operator (with integration turned off, affect position on, and timing to entry) to separate born particles. Put it immediately after your Position Icon operator.