There’s a lot of science involved with harness systems and even good belts can become a liability if installed improperly. The general rule of thumb seems to be that the angle of the harness should fall between 10 degrees below the shoulder to 10 degrees above the shoulder, with level to the shoulder being best. This is why running your harness way down to the rear belt anchors is a bad idea. The sharp angle can cause spinal compression in an accident, and that’s a really bad thing. Also, the harnesses do stretch during an accident and the longer the belt, the more stretching will occur.