So I just practiced again at my chosen location. I got interrupted. Fuck sake, people, really? Your fucking dog needs a walk at 12:30AM? Go Home!
Using a slip knot, what I am learning is to let the knot stay a little loose around your neck, then adjust, put pressure to check for discomfort, and then put some weight into it and then snug up the knot. As far as missing the trachea, try this:
Put the slip knot around your neck then move your chin down towards your chest. I am now using the back of the neck position, with the knot just a little to the let of my back bone. Lowering my chin while I find the best spot seems to work really well. As far as the wind pipe, you want the rop as high on your neck as possible, up next tot he jaw bone. (Some people say below the trachea, which does not work for me.)
In summary, you want to noose your neck with the knot near the back of your head and offset from the backbone just a little. Lower your chin and apply some pressure with the knot just a little loose, with the knot at the back of your neck. Then adjust as you put pressureon yuor neck. I would guess about an inch of space behind the neck where the knot is. After you find the most comforatable spot, then and only then, snug up the knot. For me, it is really important to move the chin down towards the chest. That brings up the rope away from the trachea.
All said, it is still painful as fuck as I put more and more weight, not on teh trachea, but just on the sides of my neck, like something is pinching me. I don't think I could do full suspension without easing into it first, blacking out, then my body goes intofull or near full suspension after I loose consciousness. In fact, that's why you see so many pictures of people with on foot still on their chosen base and one foot off. They're lowering their body down just enough to black out, this avoiding full suspnsion pain.
It sounds like you need to practice first. If you want a fool proof way, the best bet is to find a place to jump that is at least 8 stories above the ground, or about 85 feet, and the landing area is solid.