Implement and Object-To-Object Mouse Drag capability for both script and keyword tests.

I've had a similar problem and solved it by first clicking the destination cell, then determining the mouse position on screen and use those coordinates for the drag operation.

Something like this:

function informedTreeDrag(tree,destinationTbl,dragobject,row,col)
{
  tree.ClickItem(dragobject, skNoShift);
 
  var a = tree.get_MousePosition();
  a.set_X(a.X - tree.ScreenLeft);
  a.set_Y(a.Y - tree.ScreenTop);
 
  destinationTbl.ClickCellXY(row,col,10,20,skNoShift);

  var b = destinationTbl.get_MousePosition();
  b.set_X(b.X - tree.ScreenLeft);
  b.set_Y(b.Y - tree.ScreenTop);
 
  tree.Drag(a.X,a.Y,b.X-a.X,b.Y-a.Y,skNoShift);
}