Where do you set the crossover switch Power Acoustik RZ4-2000D. It has 3 positions and no explanation in the manual

 

Run it in AP or Flat to get the best sound.

 

Gannicus is correct - AP or Flat.
now, I am opening the fairing this weekend and I will change the front to HP, as my polks are getting too much of a beating in my opinion (my volume lol!).
I got lid speakers that compensate more than enough at low/no speeds and at high speeds you'll lose bass anyway.