first of all I like that you actually put back your drawing on top of the refference. That's the quickest way to see where it is lacking. And by the look of it you already saw most of the problems to improve next time. For your problem, I think your biggest problem right now is you focus too much on the smaller curves and that make you missed the bigger flow. The 5th one is your best, because I can see the right side is beautifully described with a big flow curve and the pinch on the left to balance it. But all the other you can see that you look at the smaller changes in the contour too much and miss the over all flow. I suggest you try to do what you did for the 5th one for the other, find a big curve that describe the contour the best, and then modify it a little bit for the smaller changes.