Having the opposite wire go slack is normal, depending on how you ran the wires. Concerning Ackerman, here is a link to a site that explains it:

http://members.cox.net/bdfelice/Pull-pull/pull-pull.htm

On my Katana, I crossed the wires and added Ackerman to the setup. Also, you should try to match the length of the servo arm to the length of the control horns or one piece rod, at the surface. Click on the link "Ackerman" within the page in the link above to see some diagrams.

Jesse