Currently box-shadow's trace the zone, not the clippath. A workaroudn to get a shadow that is the same shape as your shape zone is as follows:
Create a zone and apply a clippath shape to it as normal.
Create a shadow zone (a duplicate of the normal zone (same size, same clippath shape) and make it's background black or grey or whatever you want as the shadow color).
Create a (transparent) parent zone for the shadow zone. In the hierarchy menu, put the shadow zone inside this parent zone. Click on the parent zone and under filter effects (effects tab), apply a blur. (This will also blur the child shadow zone).
Now you can move the shadow zone wherever you want.