I am referring to expanding the scale of the negative. If you look at this article,
http://unblinkingeye.com/Articles/Pyro/pyro.html
you will see that the scale of the highlights are exaggerated by pyro. This compenstes for the smaller scale of the silver paper highlights. The highlight seperation effect of pyro is well documented in the literature. Look at the picture of the lightbulb in Ansel Adam's 'The Negative'