The point radius scale in the VDB From Particles must not be less than:

point radius scale = minimum radius in voxels * voxel size * 1.01

That is, the actual radius of the particle should not be less than the radius of one and a half voxels. In the opposite direction, the voxel size should not be greater than:

voxel size = point radius scale / minimum radius in voxels * 0.99

Using these expressions, you can bind parameters and adaptively set voxel size and point radius.