PhysX Bind, Clustering - Build Behavior Change

[mitchfx]

I was checking out this great grains test scene that someone posted to Vimeo a few months ago and noticed that the voronoi clustering and physX binding don't seem to behave like the rendered example.  I assume there's probably something that's changed in the operators over the last several build updates, but trying to figure out what the culprit is and how to re-introduce the nice clustering and clumping effect.  

https://vimeo.com/335055310

There's a link to download the Max scene on the vimeo page.