Granted, this setup was made in part to compare the two stereo pairs, or at least how the M/S pair worked alone.
But my way of thinking about it starts from 3 supercards/hypercards pointed more or less directly at the band and PA as a way of maximizing pickup of the direct sound component available at that recording position (think of that starting point as 3-way PAS). I then think about how to achieve sufficient stereo interest with that setup, about balancing the stereo image resulting from it, and about ways of fine-tuning the direct-to-ambient/reverberant balance. Mic spacing and the inclusion of the side 8 help with those things.
Pointing the outside pair a bit outside of the stacks maximizes the available level difference information between those two channels (based on the pattern/angle relationship), while still keeping the direct pickup of the PA maximized. Yet that on it's own doesn't generate enough pattern/angle sterophony for my liking, so mounting the mics widely enough helps bolster that with time-difference stereo cues. If using PAS to maximize pickup of direct sound wasn't my primary concern and I was outdoors with this same 3-mic starting point, I'd double that mic angle and point the outside supercardioid pair 180 degrees apart.
Turning the center mic into a M/S pair helps with the secondary concerns of balancing stereo image and adjustment of the direct/reverberant balance. It "fleshes out" the stereo image across the center, and provides non-direct ambient/reverberant sound for me to work with.
As intended and as expected, the sideways facing figure-8 picks up significantly more ambience and reverberant sound than the other 3-channels, yet all of them have a good degree of audience/room ambience and "you are there vibe" in them. It's not as if one pair provides one thing exclusively and the other pair provides something else exclusively (although increasing that often limited difference is partly the goal of many of my multiple mic array suggestions here). It's actually more like the 3 directional PAS mics provide the direct sound basis, setup in such a way as to get as much stereo interest as possible while achieving that, and the side-ways 8 lets me fine-tune image and ambient balance.
So in a way, the figure 8 serves something of the same roll as the rearward facing cardioid I commonly use (control of ambient balance - room and audience contribution), except it also provides some welcome control over stereo image by forming a center M/S pair. I often like a rearward facing mic, but it that isn't very useful from this recording position, in this type of room. This is better suited to this situation.
Not sure if that way of thinking about it is actually any more fruitful than thinking of this more as two separate stereo pairs, combined. It's just where my thought process is coming from.