I know of that prob.
It is the water droplets that couse that, Bec the box can't fall directly true antoher object, So the Droplets must move first.
As you can see at the start of the layout the 3 Box's angle are in a Sharp anle /
So that couse the box to fall more smoothly theu his first Hit!
<img src="smileys/smiley1.gif" border="0" align="middle" />
You See:
Yellow=Light Box
Green=Meduim Box
Red=Heavy Box