ackerman simple expla
http://www.longacreracing.com/articles/art.asp?ARTID=11

bump steer simple expla
http://www.longacreracing.com/articles/art.asp?ARTID=13

here is a simple article on ackerman and rc cars..
http://www.pbracing.com/handling/ack...principle.html

you can not change ackerman by changing the pivot point of the steering arm( up and down), you can create a bump steer effect because you took the arm out of the location were it was in sync with the movement of the suspension this is just exactly what you do when you move the front arm up and down on the rear suspension, you create a toe change due to suspension movement up and down,
same principles apply here.. there may be a posative effect but you are not changing the ackerman angles..