Flattening a jib (draft) is usually a matter of cut. A lot of downhaul can move the draft forward but (a) not if the sail is already roller reefed, and (b), you can't/shouldn't roll/furl the sail with a lot of luff tension because it is really hard on the bearings. The manual will recommend releasing tension before furling.
The other common method is a foam luff, which helps suck up cloth when rolling. But that has to be done when the sail is made.
Jibs that are too full when roller reffed (most of them) make lousy heavy weather windward sails because they are too full and cannot be feathered.
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Changing the angle of attack (moving the clew towards the centerline) is a different matter. Barber haulers (named for the Barber brothers) can pull the clew in, but that is typically a smooth water strategy, when you can use a high gear. Whether that actually helps depends on the conditions, the keel, and the base sheeting angles. Many boat do not benefit from narrow angles in waves; they will just make leeway. The apparent wind in waves (slow conditions) does not move as far forward for a given pointing angle as it does in lighter winds, when the boat is moving at a greater percentage of wind speed. What you need is actually a broader angle that will give more drive. You need to shift into a lower gear to drive into waves.
In fact, hauling the clew very slightly outboard and forward, and then sheeting hard, can flatten the sail and improve drive into waves (better drive angle from the sail). You want drive (low gear), not heeling.
Google "3D leads" for more information. Typically, you can bodge them together for testing without drilling holes or spending money. If they help, then tune them up.
3D leads
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All of this varies with the boat and the conditions. Keels. Base sail shape. GPS can help you figure out what actually helps you point. Pinching into waves is normally slow, but it can be smoother. It depends. Experiment.