@DrGeoff, nice recording! Great performance and handy little recorder. I will probably add one to my kit.
Mid-Side (MS) mics require a cardioid "mid" polar pattern. Note that using an omni as a "mid" element results in a cardioid facing hard left (or right, depending on your maths). This was shown by Mr. Ford in the latest video.
Using a cardioid "mid" polar, you can derive the Left and Right signals using the formulae:
Mid + Side = Left
Mid - Side = Right
Assuming the "positive" side of the figure-8 is facing left
It is interesting to note, however, that in most modern lower-cost (and even some insanely expensive) "MS" mics, the "MS" function is actually implemented with three cardioid mic elements. One facing left, one facing "mid", and the last facing right. By adding L+C, you get a left polar pattern rather half-way between the front-facing capsule and the left facing capsule, and likewise on the right side.
The reason for using three cardioids vs. one cardioid and one figure-8 is that there are few decent studio-quality true figure-8 mic capsules with which to build microphones. I don't believe that Rode makes one, for example.
It would be interesting to discover how much difference you can hear between a LMR-style "MS" microphone and an ordinary "X-Y" coincident pair.