While they can't be at the same place,
they can be at the same distance by placing one atop the
other pointing in opposite directions with their diaphragms
in the same plane and with that plane passing through the
source. BRBR

Which is great for sound arriving from a single direction, i.e. an anechoic
situation. In any desirable recording venue, obviously the distance thing again
becomes slightly approximate. In the end, everything we do is slightly
approximate anyway, so what's a few millimeters this way or that?

Scott Fraser