If you are instancing geometry with nParticles, you can use rotationPP to rotate instanced geometry on a per-particle basis. The rotation per-particle attribute is automatically created on the nParticleShape node when Calculate Rotations is on. See nParticle Rotation attributes.
To rotate instanced geometry
RotationPP is created on the nParticleShape node.
This lets you use scalar attributes, such as radiusPP, to set vector attributes such as Scale.
Selecting this ensures that your instanced geometry will be appropriately scaled to nParticle Radius.