Shadow min bias should be set low to catch better shadow detail in folds, try 0.1 as a starter.  The trick with gamma correction active in your render settings, use less lighting rather than more.  Old habits die hard if you are used to using that arrangement in earlier Poser versions.  A self illuminating sky dome, like BB's envsphere will cast additional light to your scene, especially if you combine it with IDL in your render settings.  If IBL is a consideration, then the color information used in the light should match closely with your background.  However, IBL lighting is more effective with HDR images.