That'd be where I'd start it.
Is that where yours is set at? You see, I figured I'd get multiple answers and would use the "average."
Secondly, if the sub is facing the same direction as the front soundstage drivers (in my case next to the right front M80, is phase typically 0 degrees?
Hard to say since in some cases like the EP500 the amp controls have changed. In my case anything above about the 6:30-7:00 position causes my receiver to set it a -12db. Others with the newer amp controls have had to set it closer to the 12:00 position.
I’d start at 1/4 like Ken suggested and run your auto-call and if it get set close to 0 your good. If you have an SPL meter you could just match it to the rest of your speakers which is what I do since I find that receiver auto-setups have always been of 2-3dB when I use them on the sub.
Go download and burn a Real Traps test tones CD, or equivalent freq. spectrum CD. Run through the frequencies on the CD. I do it by ear. Adjust the crossover in the amp and on the sub, adjust volume of sub, and position of speakers, to get a fairly even sound level on all the frequencies. I sacrifice in a few frequencies due to room resonance, but overall it is MUCH better than poke and hope methods. Moving speakers closer and further from back walls make pretty huge differences in sound balance. Getting the crossovers in the amp and the sub/towers correct is another biggie. There is no "right" place on the volume knob that works for everyone.