Are you shifting your weight properly.by the way you are describing it seems you are leaving your weight on your back foot and scooping at the ball with your hands and making you loose vital power.at the half swing you are already in a position to release the hands where as with the 3/4 you could be casting(releasing too early)try to maintain your wrist cock as long as possible.This is important with the irons as you want to hit them with a more descending blow.Ihope this makes sense.good luck