I actually start with 0 to make sure everything is working on first fire up, then go to -15 and compare. Work my way down from there. if you are already over powering be careful. Do you ever smell your coils?? I tried around -7.5 but seemed like too much, right now I am at -5.5 and it seems about right (thanks DD1+) in spring since I've had this set up for a year at that time I may play with -6 and even -6.5 (and everywhere inbetween to really get it dialed in). Keep in mind that EVERY set up is different, what works for one person won't work for you etc. Watch the temps of your subs, voltage, smell, etc. etc. and if the subs sound like they are too over powered etc. etc. just readjust. Have you figured out what your rise is??