Damn this is one confusing thread
Things gets really confusing by introducing spacing into the equation.
The minute you start to de-correlate information (e.g. spacing mics, turning the focus, etc), that combination effect doesn't emphasize and deminish to the same effect as it does with a coincident pair.
To explain that in a bit more detail-
If the microphones are truly coincident, the relationship between signal level and polarity is the same across all frequencies and the derived polar patterns remain consistent regardless of frequency. That's standard Mid/Side stuff and confusing enough.
If there is space between the microphone capsules, the phase relationship between the two mic signals varies with frequency and that straight-forward relationship becomes very complex. The phase relationship between signals in that case is also determined by the relationship between the wavelength of the frequency in question and the microphone spacing.
Now down the rabbit hole, Alice-
Now, what you *really* want is 4 channels, 2 cardioids coincident to each other, 180 degrees apart, and record stuff in what amounts to a B Format. Invert the rear facing ones on each pair and you can adjust your pattern (but not angle) by adjusting the volume on that back "lobe." Be a baller and go for 8 channels and run two sps200s (adjust angle and pattern, but not spacing).
I don't know of any way to adjust the spacing later using just room mics; I've played with doing specific delay timings later in post on coincident pairs and it just doesn't work like I want. Mathematically it makes sense why it doesn't (tldr; I want to delay some sounds but not others), but that's the last limiting factor. You can do it with spot micing easily enough though (dupe the channel, adjust panning to "place" it, reduce the volume in the "other" channel, then add fractional milliseconds of delay to get it to pop out).
All traditional B-format manipulation is standard Mid/Side matrix math with more channels than two, and like Mid/Side is constrained to first-order patterns (no magic lobe elimination possible), but gains the freedom to derive patterns and the directions they point independently of each other.
Using traditional B-format matrix techniques there is no way to simulate spacing. The virtual patterns are always coincident. The only way around that is actually putting microphones in two separate locations as Page suggests with two Soundfield mics. That only gets you that one particular spacing however, it’s not adjustable later like the polar patterns and angles.
The possible paradigm changer is using advanced analysis and manipulation techniques other than standard matrix mathematics. There is a B-Format decoder now on offer called Harpex, which uses advanced techniques I don’t pretend to understand well at all, that simulates the spacing between virtual mic capsules and higher-order patterns. It simulates near-spaced configurations, spaced omnis, greater than 1st order supercardioid directionality and horizontal only HTRF simulations. In a way it becomes trickery instead of pure Mid/Side matrix mathematics, but if it’s convincing and gives good results maybe that doesn’t matter so much. As I understand it the technique slices up the audio in to thousands of frequency dependant bits and determines a direction vector for each, then does something like Page mentions.. probably applying source direction specific delays and M/S matrixing based on each frequency bin before putting Humpty Dumpty back together again.
I’ve not tried it yet myself but many in the ambisonic recording community speak highly of the results on the sursound mail list and at Gearslutz. As you might imagine, very few using it really understand the basis of how it works, but the interface is easy and visually informative. The AES article and patent describing how it works is linked at the Harpex website, and is written in typically obscure patent language. If anyone does B-format work and is interested they have a trial download and a page that lets you upload and decode small samples to get an idea of how it sounds. It’s not inexpensive, and so far I’ve resisted the urge to spend enough time to check it out.