Okay, I know this has been addressed before, but to me it still is unclear.

One post said that the phase setting which results in the louder sound is better, another post said to adjust for the best blend with the mains. The manual says to choose whichever position is bass heavier. Frankly I don't see any difference with any of these three criteria.

Is there any more objective means of setting this switch??

This may not be the answer you're looking for but it is a start...I leaned over the top of my LFM-1 while something "bassy" was playing...it sounded AWFUL from this position by the way...I switched back and forth but only once...one of the two positions "seemed" more powerful in the bass department...I then sat back and it sounded great from my listening position...of course, it wasn't bad prior to "changing" or properly "phasing" the sub.
I hope this helped.
Bill

Thanks....

Believe it or not, your suggestion seems to me to be a better one. I will absolutely give it a try.

I was able to listen to the pure sw output (with the other speakers turned off (the amps driving ft, center and rears was off, while the sw was obviously on). This was, it was clear that I was judging from purely the sw output.

The phase switch in the 100 degree setting was a bit louder.

(Don't know if this is correct, ie if I need the main speakers to be on in order to tell)...

It seems to me the only way phase is important in in the context of other speakers, so that they can be "in phase" (sound waves piggy back on each other), or "out of phase" (waves cancel out).

I'll try to isolate and test my SW to see if I can tell a difference.

Interesting.....

I would agree logically....however, I absolutely noticed a difference with the two settings, even though all of the other speakers were off.