The flux density in the magnet will be reduced because the
flux in the magnet is no longer passing straight through the
magnet from end-to-end but is “leaking” back around the
magnet itself. Because this leakage of flux is in the opposite
direction of the internal magnet flux, it has a demagnetizing
influence on the magnet. As the air gap in the circuit
increases, the leakage flux becomes greater. As a result, the
magnet flux is decreased.
How far down the demagnetization curve the magnet flux
moves will depend upon the air gap size and the geometry
of the magnet.