I trade e-mails quite frequently with Jeff Scott where we discuss weightlifting technique and training progressions. Below is a recent exchange we had about the jerk and foot placement.
Q (Me): On stepping through in the jerk: Since the initial movement (dip/drive) needs needs to be as close to vertical as possible, how does one best attain a sufficiently forward foot placement when there should be little movement in the horizontal plane?
It often feels like my foot can only go so far in front relative to where my torso is. Do I need to work on pushing myself forward under the bar once it has been thrown off the shoulders?
A (Jeff): Some would say that since the jerk should be thrust upwards and backwards, there is no need to step forward. Dennis Reno offered photographic evidence vis-a-vis Ilya Illin that showed him with no forward displacement of the front foot. His split was strictly down and to the rear...or at least it appeared so in the photos. Wherein lies the truth?
Joe teaches the step through technique which is predicated, in part, on the assumption that when the weight is very heavy, it will slide forward and the throw will be forward too. If you always throw it up and slightly back, then your forward displacement can be less pronounced. The jerk is very technical and few people practice it enough to become very proficient at it. If you are having technical difficulties in your jerk performance, I would suggest more jerking and more exercises to help the jerk. Make it a movement of emphasis for a twelve-week cycle and see what happens. If you aren't doing any concentrated work on the jerk as a movement unto itself, then it is difficult to draw any meaningful conclusions about your technical issues.
The most important thing is this: do you lose most of your jerks to the front or to the rear? If it is to the front, then you need to step through more. If it is to the rear, you may be stepping too far forward and/or throwing it to the rear too far. I think from observing you that you lose most of your jerks to the front which means you are throwing the weight slightly forward and "short stepping" your split. The weight is not aligned in a vertical plane with your hands-shoulders-hips. The only way to correct this is to mark the platform (chalk, for example) and split to the markings, front, rear and sufficiently sideways, every time you jerk...or throw up and back to the same point every time.
Also, consider this -- what exercises, other than the jerk from rack and C&J do you do to improve your jerk? Are you doing jerk drives? Are you doing jerk supports? Are you doing behind-neck jerks? Any partial front squats? If the answer is none of the former, then you are not doing enough to improve your jerk.