A neutral plate position is normally level with the bottom of the cone, this is adjustable by bending a small clip / spring that acts as a stop at the bottom of the unit. The purpose of this spring is to allow the flap to move beyond its neutral position to allow excessive pressure to escape if the engine was to backfire, passing a large volume of air back into the air filter housing.
If the system did not have this facility the pressure could split or blow off the rubber air trunking. Any splits or ill fitting air hoses that allow unmonitored air into the engine require rectification.