Okay, I've been thinking about this for a bit. If you match the coating IOR to the wood, you essentially reduce the reflection occurring at the surface of the wood. I think that has the effect of enhancing contrast because only the most favorable reflections will make it to your eye. That would also increase the chatoyance because the reflections are sensitive to angle. So basically the funny bits that aren't flat (i.e. the figure) get darker. Is that about right?