Intuitively is right, but in practice you will find it fogs and does not increase DMAX. This is because with the higher concentration of metal, it begins to reflect back light no matter the exposure, thus creating a base fog that has a slight shiny appearance, less contrast, and quite the drain on the wallet. I've seen this numerous times at B+S. If you want increased DMAX that is very apparent and real, try some fumed silica.
Thanks - I guess that you've saved me a lot of hassle :-)