Now that you posted the image, the problem is more clear.
Property Test > Neighbor count. Forward direction > particle Z. Search radius > shape radius. Look ahead > the voxel size of the Birth Voxels operator. Test value > less than 1.
Property Test > Neighbor count. Forward direction > particle Z. Search radius > shape radius. Look ahead > the voxel size of the Birth Voxels operator. Test value > less than 1.