The fact that you can not obtain a good solid bale confirms my suspicion about hay movement.
Lets go back to windrow formation. The more uniform the windrow, and the more uniform the amount of crop flow into the baler, the more uniform the bale shape, bale length, and tying will be. Where crop fails to fill the top of the bale, increase the size of the windrow by double raking or combining windrows. Operate the baler at 540 rpm and adjust ground speed to maintain a consistent and even flow of crop into the pickup. Ground speed and crop flow that produces 14 to 16 plunger strokes (bale slices) per 36 inch bale, or 15 to 17 slices per 40 to 42 inch bale will produce the most uniform bales. As the windrow size varies, adjust the ground speed to obtain the proper number of slices per bale. In extremely light / springy hay consider bale chamber liners in addition to the hay restrictors.