Nice pics D  When they are running straight there angle to the a-arm changes quite a bit threw it's range of travel and causes excessive bumpsteer and toe gain and lose. When set lower and running parallel with the arms they stay much closer to parallel with the A-arms throught the suspension travel range reducing bumpsteer and toe changes. With some varying thickeness spacers you can get it to almost no bumpsteer, each bike would be slightly different on thickness to get almost 0 bump.