I may be completely wrong about this, but in my experience when you adjust your ackerman so you have less, meaning the difference in steering angle between the inside and outside wheel is less, this can make the car feel more mellow, as it causes less variation between your low-speed turning circle center (near the back of the car) and your high-speed turning circle which is toward the center or even front of the car due to the higher weight transfer of turning at high speed and allowing the 'slip angle' into account as the back end slides.
That being said, I don't know what denotes + and - in the opinion of Yokomo. I adjust ackerman with the angle of the front links. If it feels good and turns good laps, fantastic.