The slider doesn't affect the transparency of tokens, it merely lessens the veil of things like dynamic lighting. Roll20 Wiki says: The fog appears as a solid black area to players, but for the GM it's a semi-transparent layer. If you'd like to adjust how dark the fog appears to you ( handy for dark maps where it's hard to tell where it is ) use the "GM Opacity" slider to adjust how transparent or opaque it appears. Simply slide the slider to the left to make the fog lighter, or to the right to make it darker. If the slider is all the way to the left, the fog will be completely invisible, and if it's all the way right, it will be completely solid. Could you supply a screen shot of the issue as you are seeing it (preferably on a blank test page with some examples of tokens on both the token and GM layer and maybe with your overlapping map issue in one portion too)?
