Good point, Ron. I'm so much older than stereo, I forgot!
Let's approach it from the time domain:
Assume your ears are 0.2 meters apart. Assume the sound source is 5 meters from your head. Assume the speed of sound at your location is 345 m/sec (ref. Wikipedia)
Now a displacement of 5 degrees of the sound source left or right will create a relative displacement of the source to your ears of +0.00971 and -0.00772 meters, or a total relative displacement of .0174 meters.
Given the speed of sound, that translates to about a 50 microsec displacement.
I'm sure golden-ear audiophiles will claim to be able identify sound sources to a much greater accuracy, but I really could not give a darn if the clarinet section all moved one or two seats to the left.
But, back to wire length. Assuming about 200,000,000 meters/second, 50 usec translates to about 10 km. That backs up what you said, Ron.
Analysis in the phase shift domain at 20 kHz will give different answers, if you assume small acceptible phase shifts. But, the wave length of 20 kHz is so short, (about .017 meters, or 1/10 the distance between your ears) that it is, for all practical purposes, impossible to locate a 20 kHz source with your ears. Have you ever tried to trace the source of, say, a 15kHz squeel?
-My two bits,