Appropriate particle to cell width

Hello Friends, I'm working on a CFDEM setup in which a cube is filled with a few particles such that the particle to box volume ratio is 0.6. The fluid domain (please see attached images) has all cubic control volumes. I have tried two different cell widths.

1. cell width = 1.162*partDia. This is from the documentation that the volume ratio of the biggest particle to the smallest cell >= 3.
2. cell width = 3*partDia. This is from articles.

I'm using voidfraction divided model with the following properties.
dividedProps
{
alphaMin 0.01;
interpolation false;
}

When I see the voidfraction range for the fluid domain in paraFoam,
for (1): it varies from 0.038 to 1 as seen in fineMesh.jpg.
for (2): it varies from 0.27 to 1 as seen in coarseMesh.jpg.

What is happening here? How to decide appropriate cell width based on particle size?

Thank you,
Jagan Mohan.