Volume Sample RBD collision behaving oddly

[richard_mcd_green]

Hi,

I have an RBD simulation that drops petals onto a piece of terrain.

I've created a collision SDF for the geometry, but for some reason it is behaving strangely and the petals are colliding above the surface, even though the Collision Guide looks fine.
Is there something I'm missing here?

http://oi65.tinypic.com/2zrp2y9.jpg

Shot3.hipnc

[Skybar]

Using bullet? It doesnt use volume collisions and uses convex collision by default. See the guide geometry under the bullet tab.