Evaluating headunit distortion with distortion detector

I used an smd distortion detector last night. The detector shows that my headunit is distortion free up to volume level 33 out of 35, which means level 33 should be used as my max volume for setting my amp gains. does this seem correct? It just seems high to me. I've always set max volume at around 80 percent, but the detector is telling me I can go much higher with this headunit, which is an alpine cda 9886m. I tested it a bunch of times with the applicable tones and it was the same every time.