How to make the dif shadow sharper?

Hi,
(I am not sure whether it is the right place to raise the issue...)

And I'd like to ask anyone who have dealt with the interior shadow before;

We have a room, the walls, celling, floor and window are created in .dif format and other small furniture are in .dts;

We have realized to cast the window's shadow onto the floor and all the dif parts can be auto relighted according to the 24h's daylight changing, which simultaneously affect the window shadow's position;

And what we want to improve is the sharpness of the window's shadow; Thanks Ryan Mounts to instruct me to reset the light_geometry_scale to 2 to increase the sharpness in some extent; and we also find commented out sgColorMap::sgBlur() function can make the shadow even shaper but the edge of the shadow has very clear sawtooth;

So, if we want to further improve the window shadow's quality (to make it clearer and sharper), does anybody have any methods?

Thanks a lot...