Dragging a Camera along a plane / Where's the error?

I'm trying to drag the camera with the mouse (respectively a finger-touch) along a plane. But for some reason the camera doesn't move in the same speed as the touch is moving relative to the scene. It moves to slow. I have no idea what is wrong in my code:

 float distance;
 
 //Getting the ray pointing towards the point in the scene, relative to the screen-pos
 //The camera looks straight down to the scene (a floorplan)
 Ray rayNow = m_FloorPlanCam.ScreenPointToRay (finger.position);
 //Getting the distance from ray origin to a plane (which is Plane(vector.up, vector.zero))
 m_FloorPlane.Raycast (rayNow, out distance);
 //Now getting the actual point in the scene
 Vector3 planePointNow = rayNow.GetPoint (distance);
 
 //The same as above for the previous finger position
 Ray rayBefore = m_FloorPlanCam.ScreenPointToRay (finger.position - finger.deltaPosition);
 m_FloorPlane.Raycast (rayBefore, out distance);
 Vector3 planePointBefore = rayBefore.GetPoint (distance);
 
 //The differens between this two points in the scene give me the amount to move the camera
 Vector3 sceneMove = planePointBefore - planePointNow;
 
 m_CurrentCam.transform.position = m_CurrentCam.transform.position + sceneMove;

Thank you for your assistance.