As far as I know:
Ackermann: Looking as a driver in the car. Putting the steering rods more forward and therefore less shims at your servo saver, and give it a negative ackermann value gives more initial steering, but looses a bit on mid corner and corner exit. It helps to settle the car down.
Reduce the shims and give it a positive ackermann value gives more ration, but less initial. It will make the car feel agressive "inside" the corner.
Bumpsteer on the other hand is the amount of shims on the steering hubs (when you keep the servo saver mounting point the same) Making it more a roof shape "^" so less shims on the steering blocks will give it more steering when compressing the suspension. So when hitting a dot, or a bubble in the carpet the car suddenly gets more steering. The car will feel twitchy but this can give you more steering if you want
When angled more like a bowl "V" shape. So a lot shims on the steering block will give a smoother feeling. It will not change the amount of steering that much cause it is following the angle of the upperarm.
So: Looking at ackermann I Personnaly try to run the rods as straight as I can. Then, when running modified I put a 0.2 shimm behind my servo saver, so it gets a little bit negative camber. Running blinky stock I don't put that shim there.
When looking at bumpsteer I try to follow the upperarm angle as much as I can. This will make the car more smooth. But not forget, all is up to a point.
Regards Robert