did you find a trick with bitmask collision group/categories ?
Just gave it some quality time, and I think I've solved it. Check out the latest code to see if the example is doing what I think it should be now. (all small shapes collide with everything, large shapes don't collide with each other. large rect doesn't collide with triangles at all ??)
here are now 3 physics modules
and of course there's also that PhysLite, although it's not as free as those other three.