ZBrushCentral

Dynamic Simulation - issue

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For some odd reason, this simple Dynamic test doesn’t work

Result: After running the simulation and collision is on:

as you can see, the plane just falls through the face mesh and doesn’t seem to detect the collision object at all.

I tried a more dense mesh, and subdivided both, here is the result:

The plane again, “goes through” the face mesh on the bottom.

I am sure I am missing something fundamental here.
But what is it?

Thanks for any help,
appreciate it!