<Pivots>
<Pivot Pos = "0 0 0" />
<Pivot Pos = "0 1 0" />
</Pivots>
Where posiion order is: "x z y".
Also if i remember correctly when you export object from 3d program, its center is center of the world, so in game <pivot Pos="0 0 0"/> will be location where center of the world was when you exported object.
I think you can avoid that gap you have if when your object_height % levitation_VStep = 0.
% stands for Modulus.
Hope that sounds understandable to you.
