Just the basics' I have no clue as to what a GSS is but assume it is some sort of low wing airplane. typically if you try to balance a low wing right side up there is to much mass above the balance pivot and any balance point derived at like this is suspicious at best.

Here is the bottom line using your finger or any kind of mechanical device there must be more of the airplane mass below the fingers or contact points on the device. This assures positive stability which must be in place or you will never be able to acheve an accurate actual balance point.

John