poser works well with hdri (0 <= rgb <= 32) on bill's envsphere.  when using ones with visible sun, area subtended by sun and glare around it (rgb >> 1) is too large for sharp shadows.  FFRender calculates transition from sharp to blurred sun shadow using raytracing, like when horizontal occluder casts shadow on vertical surface.

other advantage to using inf. lite for sun in poser: kills IDL corner artifacts whilst allowing speedier renders (interpolation and low samples).