Distance between forward-facing pair is 1/3 the distance to stage.
what does this mean? He's using cards...
This is the way it was explained to me, I'm not sure that I know it well enough to teach, but here goes:
Spaced cards or spaced omnis, shouldn't matter if the cards are pointing straight at source.
It's the time differences as opposed to the time AND level differences of DIN, ORTF, RAI, OLSEN, etc.
Angling a directional mics causes level differences due to distances (angling an omni does nada)
Hence coincident X-Y creates stereo, without spacing.
The physical space between the mics creates the time differences.
Hence Spaced mics create stereo, or their angled stereo effect is enhanced by near-coincident spacing.
Either time or level or both create the spatial effect. For us two-mic'ers, that's the stereo effect.