I did a lot of tweaking on my car last year to solve your problem...
I put two washers under the ackerman plate, and then put a JR servo grommet bushing, flange side down, on the knuckle. You'll have to get some new rod ends. I found Mugen MBX-5r rod ends (#muge0814)worked the best because they're bent. The JR bushing is so there's no binding, because even in stock form, the old rod end would bind on the spindle. When you do this you'll also have to get a long screw and nut and replace the original flanged pivot ball with a round one.
After all that shimming you'll also have to grind some of the front arms away so that the steering is free even at full compression. You'll see what I mean if you try it. Once you do all that the car is very predictable and easy to drive.
Later
Alex