Ok, my 2 cents:
Q: What's the hardest thing about flying headdown?
A: Holding the headdown position.
ok. guess what. WRONG!!
Headdown isn't about holding the magic position. There's no such thing. You angle your body to accomplish your needs at the time, be it forward, backward or side sliding movement, steep tracking, etc. I think this is part of the problem that makes headdown seem harder to learn than it actually is. Too many people trying to hit a position they think is correct, and wondering why they don't stay headdown.
So, here's my suggestions/exercises (it's called the "pendulum" exercise):
Leave the plane. Belly to earth. Slowly de-arch. Bring your arms in (all the way - you won't be using your arms yet). Straighten your legs. You'll slowly go head low. Allow the relative wind to take you onto your back. Now arch. You'll slowly return to a headdown-ish position, and continue onto your belly. Repeat.
Important things to note/do:
1. Keep your head level, eyes straight ahead. This will allow you to observe where the horizon is relative to your body angle/attitude. Be very specific about this.
2. Keep your arms in the whole time.
3. Do this exercise perpendicular to jump run. At 6k, stop, go belly to earth, check your position relative to jump run, check below you, etc. Track or deploy if necessary (you flew up/down flightline, or someone is below you, blah blah...).
4. Repeat this jump 3 or 4 times. Then repeat it again, this time with your arms out.
5. Lastly, and importantly - let the relative wind do the work. Even if you go severly onto your back or your belly, apply the proper arch/de-arch, and let the wind take you back over. Even if it takes some time. In fact, that's the point of the exercise. Don't try to stop the pendulum movement short by trying to stay headdown. Instead, do go all the way past headdown each pass thru the pendulum. Later, when you're better, you'll just use body torque to bring yourself quickly into position. But this exercise is about 3 things:
A. Learning/feeling the relative wind and how it works in relation to headdown flying.
B. Not concerning yourself with the mythical magic headdown position.
C. (Similar to A) Learning how to move your body relative to the horizon to adjust to the desired angle of flight.
So, all I can say at this point is, try it for a day. You should do say 8 or so total jumps doing this exercise. 4 with arms in 4 with arms out. Does it work? Yes. It's helped a lot of people, and I used it when I first learned to fly headdown.
Oh, and keep doing visualization/meditation. Lucid dreaming helps, too, but enough of the hippy talk - go out and try it :)
