I'm sorry if you get this kind of question regularly, but I have been having a lot of problems with this. I have watched several videos on this topic (several times) and for the presenter its always click click click and perfect results! Unfortunately I don't know if my problems are lack of skill and experience or if there is a setting somewhere which needs to be switched on or off and I have yet to find it.

In the attached picture you can see genesis 2 female with a dress from DAZ3d. I have highlighted what I think are the important check boxes in red. I have also indicated that I have selected the general cloth properties. I have applied a weight map that I made myself in photoshop. As you can see, the lower part of the dress (where the weight map is white) passes through the figures legs.
It was my understanding that the weight map affected the physical properties of the softcloth (elasticity, mass etc) not the collision properties. Is that correct?
If I dial the brightness of the weight map down until it is very dark grey then the pass though is less. That seems to suggest that the weight map is affecting the collision. If that is so, how is it possible to get a very soft cloth that does pass through the figures body? I know that it is possible to add Collision Shapes to a figure. Is that the answer? I surely hope not. I hope that the mesh of the figure itself can be used as the rigid body.
Any advice would be welcome.

.75% of original size (was 670x19) - Click to enlarge