Here's something to remember, a lot of pictures you see of people are not correct jumping positions! Yes, even pros, grand prix jumpers, students of great teachers. Jumping is hard and it takes a while to be completely secure and correct over the fence. And even those who have good positions can develop bad habits. Laying down on your horse's neck, or "ducking", is NOT correct nor ideal, but it is a very common bad habit so you see a lot of people doing it. You need to free up your horse's front end/neck and allow your horse to jump. It inhibits their ability to balance or use their body well. I would have to disagree with MyBeau. It's not how hunters are supposed to be and judges don't reward you for it (they may give out blue ribbons to riders who have a better round then the others despite the ducking though)
If you really want to know more about jumping positions I would highly recommend picking up a few copies of Practical Horseman magazine. There is a monthly article called "Jumping Clinic" where George Morris evaluates 3 riders positions, explaining what is wrong, what is ideal, and often goes into explanation of why. Very informative!