Bantios
Reason being: The extra lift created from flap 40 gives you a high nose up attitude and causes a baloon effect just as you flare.
Are you sure? In the 737-200 /300 and /400's I flew the opposite was true.
The approach at F30 would be about 2.5deg Nose up vs F40 at 0 deg Nose Up - ie lower nose attitude with Flap 40 set. As for a balloon effect with Flap 40, would have to disagree there also - the greater drag causes for the aircraft to settle quicker than with Flap 30 when you close the thrust levers.
Maybe the 737NG is different?