My favorite is when someone installs the shoulder harness/belts through the stupid holes in the seats and they come out below your shoulders, during an accident, you will get spinal compression. Always have your belts positioned above the shoulders just slightly to minimize the angle and stretch in an accident.
I will agree, the belts should not be excessively pulled up or down by the opening in the seat. Ideally the belts should be deflected very little by the seat between the drivers shoulders and the mounting point and I've changed the openings in the seat to correct this for tall or short driver situations. Beyond that, the mounting locations for belts in racecars are pretty specific and spelled out in the rulebooks.
