At the risk of putting out bad/misleading information and getting spanked, here's the best explanation I've found about GI. It's for Cinema 4D, so the settings may be different from Poser but it does give a good idea fo what the pre-pass is doing and how the distribution of the points relates to render quality. Hopefully it will roughly correspond. Mouse over the Settings, Point Distribution and Results labels under each image.

planetpixelemporium.com/tutorialpages/global.html

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