You can use different halftone settings.  That looks like a large dot size.  The Edge2 can go pretty fine.  Try setting the halftone setting to a finer setting.  The trade off is usually in gradients though.  Larger dots give smoother transitions in larger printers and smaller dots will give more banding (I know, it seems a little backwards, but that's how it is.) If this is just a shade of of a color that remains constant, you should be ok though.  Another option is to use a spectratone combination to get lighter shades.
Good Luck,