Iyad Horani posts a really great 5 part look at understanding reflections in Softimage and getting better more realistic results when rendering in Mental Ray. Iyad notes that this was originally supposed to be part of a training package for a publisher, that never saw fruition.
Although this section is a couple of years old, it is still relevant to the current versions of Softimage, and not a bad watch if you are really looking to understand all the settings and fields associated with mental ray reflections and their results.