The QB completion % is the result if a mix of sliders, not only QB accuracy and pass coverage. I have HUM pass coverage set at 0, pass reaction at 3 and no CPU QB have ever had a game with 80% completion against me. I think you should mess around a bit with OPI, DPI among the others. I'm not sure how I came to the results I see when I play but finally I managed to find a set that plays really well. The only thing I have to understand is if I can drop the HUM INT slider without affecting the coverage.