I have heard teachers talk about cutting along the diagonals, does this ring a bell?
I'm not sure if it's been mentioned, but there's a good Shinto cosmology at the Tsubaki America web site regarding
, if you're interested.
Also, to me it sounds like maybe you're describing the shikaku (dead angles). For example in the forearm, relatively speaking the ulna and the radius can be thought of as constituting a "vertical" axis; perpendicular to that axis would be the "horizontal" and bisecting those axes are the shikaku...as I think I understand it anyway. Theoretically, your structure should be strong to the sides even when you're facing forward. The example I'm most familiar with is a static stance where you have someone push from the front, back and sides (shoulders/upper arm), then they push on the shikaku and the posture begins to twist.
Then again you might be refering to the idea that it's harder to side-step a diagonal cut than a vertical one?
At any rate, one thing that sparked my initial interest to Aikido was the beautiful geometry. Reading Aikido and the Dynamic Sphere did a lot to give me some of my initial appreciation for Aikido.