The first part, where you have to move the lever through its travel, is because the implement prevents the lift arms from fully dropping. So when you move the lever to "0", the lift piston fully contracts and the arms stay lifted slightly. The 1/4 of the way through the arc is taking up the "slack" left in the piston. If you raise and lower the lift arms with no implement on them, you should find that they begin to move pretty much immediately as soon as you begin moving the lever.
The second part, where it's jerky... I have found that to vary depending on how heavy the implement on the 3ph is and what my engine RPMs are. Lower engine RPMs provide a smoother travel. I have also found that moving the lever decisively helps. In other words, instead of nudging the lever, then nudging it some more, begin moving it and continue moving it smoothly to the position you want to go to.
That's fine if you know what position you want to go to. For example, if I want to raise the box blade all the way up for transport, I just pull the lever all the way to the "10" position and it smoothly lifts--no jerkiness at all. But if I need to fine-tune the position of the implement while working, I can avoid the jerkiness with a little finesse on the lever. Don't start the lever moving all suddenly; rather, kind of "ramp up" the motion gently to give the hydraulics some time to catch up with you. Bear in mind that a 350-1000 lb implement has a lot of momentum. You can't just sling it around and not expect some jerkiness.
