The position of the centre of pressure varies with α. The centre of gravity remains fixed at around 30% MAC.
For a typical aerofoil with (CL/CD)MAX of around 21.6 at α = 4°, the centre of pressure will be slightly ahead of the centre of gravity, requiring downforce at the tailplane for balance - e.g. at high IAS. Whereas at low speed and α= 18°, there will be an upward force at the taiplane for balance. To ensure that the aircraft remains stable, longitudinal dihedral is used, so that if the aircraft is disturbed, the change in restorative tailplane force is sufficient to ensure positive longitudinal stability by preventing divergence.