[Otto]

I normally just determine the distances with a tape measure and set them in the pre/pro or receiver.

You can play with phase via distances, but I'd recommend getting things up and running in general first. Do some measurements with REW and see how your response looks around the crossover point. Of course, you can adjust your distances and do measurements to see if that improves things first; it's free. My experiments have shown that I didn't get much of a change from modifying distances in my preamp. Of course, you may have a different result.

From there, I'd go with the BFD to clean up your sub response.