The wing needs to be making some lift when its running along the top of the water. The floats are rigged so that the wing can rotate enough to get takeoff angle of attack. In the past I have always recommended people rig their planes so that the wing is 3-5 degrees positive relative to the tops of the floats. Not all floats are flat on top. But, if you set the plane on a tabletop, sitting on the floats, the chordline of the wing should be level-parallel to the planing surface of the float. The step is normally a little behind the balance point of the plane.