Sheet formation system and method for reducing wavy edges in a fourdrinier machine. The system includes a headbox having a nozzle bring adapted to produce a pulp suspension jet across a width of the machine, at least one rotating screen positioned to receive the pulp suspension jet, and at least two deckle plates adjacent to the screen. The deckle plates may be adjustably positionable such that a distance between the deckle plates and a centerline of the screen is adjustable in a machine direction over a substantial portion of a length of the side shields. The method includes directing a pulp suspension jet onto the rotating shield between the deckle plates to form a web sheet, moving the web sheet in a machine direction, and adjusting a distance between the deckle plates as the web sheet is moved in the machine direction. The method also includes positioning the mechanical deckle plates having a flat surface being adapted to face the pulp suspension in the pulp suspension application area to form edges of the sheet being formed and bending the flat surface of the mechanical deckle plates as the formed sheet travels in a machine direction.