In any aircraft the tail enters the ground effect first which causes a pitch down and flare prevents that, then when thrust is brought to idle the THR/WT couple causes further nose down and pilot controls it to touch down at appropriate rate of descent. In Airbus FBW normal/alternate law ELAC will oppose this to maintain flight path and any flare will be a g demand that will keep the aircraft pitching up unless stick is neutralised. So to get cosistant landings a flare mode was created in which stabiliser freezes at 50ft and ELAC causes a steady pitch down to make attitude to -2° in eight seconds. A321 being longer the arm from tail to center of pressure is longer causes early pitch down down at sufficient rate not requiring computer assistance. So the flare mode is made to start early at 100ft. freezing the stabilizer and let aerodynamics to take it's own course.