I believe the sympathetic strings should be tuned at least equal to, if not higher than the unsympathetic (they're so mean) strings are tuned. They shouldn't be lower. I've never worked with sympathetic strings but I'm just pulling this from what I know about the overtone series. If you have access to a real piano, depress the sustain pedal and play a low note. You'll hear a lot more overtones than if you play a higher note because if the strings are lower than the played note they won't resonate as well.