[A]s the Schoeps website says about the MK8, "directional pattern
almost completely identical at all frequencies." Every fig-8 mic
can share the exact same description, because they're all unequal
front-to-rear, which translates to unequal left-to-right in MS.

The degree of front/back discrepancy in figure-8 microphones varies
from design to design. For example, Royer has two basic models of
ribbon microphone: one for pop and one for classical (more or less).
The "classical" one is highly symmetrical front to back, while the
"pop" one is not so much, and the company is quite open about this.
The "classical" model also has the flatter frequency response of the
two models through the midrange and upper midrange. It would thus
be preferable all around as the "S" microphone for an M/S pair.

I have some special interest in your remarks since I'm the primary
German-to-English translator for Schoeps, and those are my words that
you're quoting. Small response discrepancies do show up between the
front and back lobes of a Schoeps figure-8. But discrepancies of that
magnitude show up when you run the same curve twice in a row without
changing or moving anything, so that should be taken into account, too.

I'm looking at the factory frequency response curves for my own MK 8
capsules, using the same pen and paper speeds that Schoeps' engineers
use for their own research, not some idealized version of the curves
for marketing purposes. (Or OK--I was looking at them a minute ago,
then I put them down because I can't type while holding them, but they
are the real curves.) No discrepancy between front and back is visible
on the chart recorder until you get above, say 3 kHz, where there are
occasional burbles of some fraction of a dB or so--up to maybe one
whole entire dB (horror of horrors!) above 9 kHz.

Given the margin of measurement uncertainty, these are effectively the
same curve to within 1 dB--and below 3 kHz they _are_ the same curve.

This is leading towards a debate over whether two matched cardioids are in
fact a truer match than either side of a fig-8. I'm of the opinion that the
matched card's are a truer match, mostly because you can't as easily test
the internal bipolar matching on a mic-by-mic basis like matching two
card's. In particular, when two card's achieve a null result under
opposition, they can be trusted to be matched in both mechanics and
electronics with extreme precision. It's impossible to test both sides of a
fig-8 with that level of precision. All you can do is "read curves".

It's still a moot point though, you really need spaced cardioids
to get the time differential aspect of natural imaging.

That's the direct opposite of what most people in this field believe,
and what several decades of live recording experience tell me.

Whenever you play a recording back through loudspeakers, you get the
same arrival time differences between the listeners' ears as you would
get in the original sound field. You don't need to create arrival time
differences between channels by spacing the microphones unless you're
recording for headphone ("binaural") playback. Otherwise it's an option
if you like the resulting sound, but it's not any kind of necessity.

I certainly hope that's not what most people in this field believe. You do
get time differentials from the separation of loudspeakers, but it's hardly
"one size fits all". To say spaced mic techniques are only appropriate for
binaural playback is as obtuse as saying coincident mic techniques are only
good for separated loudspeaker playback.

In particular, spaced mics can offer a sense of space that coincident mics
can't, since lateral sounds, in particular room ambience, result in greater
time differentials, producing a greater sense of width without comprimising
the coverage of the center signals, which for coincident mics means sending
the center signals further off-axis or widening the stereo recording in
mix/post.

There are times to add space between mics, times to widen the angle between
coincident mics, and times to narrow the angle and widen in post. Distant
micing of acoustic instruments generally means adding space IME. When a
sound reinforcement system is involved, coincident mics are imperative,
since spacing the mics generates very unnatural correlated differentials
from the separated sound sources putting out the same signal. When you have
a broad ensemble of acoustic sources, you end up somewhere in between.

I'm somewhat surprised at your opinion. Normally I'm trying to tell tapers
not to use spaced mics for concerts with PA's...