Seems I'm a little late :) sorry about that.  The displacement trick is awesome, an excellent idea and solution.

otherwise it's a combination of mesh density, as previously mentioned and collision offset.  Collision offset defines how far your mesh will get to your cloth.  If the mesh is too low a density then you will need a higher figure, probably somewhere between .5 and 1, with a higher density you can go below .5.

If you are getting poke through at a collision offset at 1 then the mesh is too low.

That said :) the displacement trick is really awesome, I'd go with that :)

John.

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