Yeah, you want the shackle to be pushed back a bit. I like it just a hair back from verticle.
Think of it this way. When teh shackle is forward it has to push it back to center, in order to do that the spring eye at the shackle must move downward (the opposite of the way it wants to travel), once it gets past center all it must do is push teh shackle back and the eye will go upward (the direction it wants to travel).
By correcting the shackle it'll smoothen the ride out. I liked my old setup where the shackle was just a hair rearward of verticle because I had maximum range of movement available to me. To be honest I'm not sure where my shackle sits now, but I think it's a bit further rearward than it used to be (I know it's not sitting forward).
Sequoia, very very bored Sequoia.