When the big piece of "slab" thing (the thing in black) has a gimpact proxy and so as the L-shape thing, all collisions work fine except that it is extremely slow.

When I replace the gimpact with hull for the "slab" thing,  when the whole object is hitting something, that something is when the L-shape thing can actually pierce thru another gimpact with some holes in it. The thing getting hit just "fades" back a few steps...

Because the hull shape is made of some convex triangle shape, the L-Shape thing is concave, and I don't know how I can break it down into 2 convex shapes, because it is one node...

But why hull shape is not working for this case?