While I am unsure of your question about the background, I can answer your Math question about the setting Triangles.
For a finished 10 " block size according to EQ, four setting triangles for the sides can be cut out of a 15 3/8 inch square with two diagonal cuts (an X so to speak).
Two corner triangles would be gotten by a single diagonal cut on a 7 15/16 inch block. That would be in a perfect world - lol.
That being said ... I would never cut them that close. 15.5 and 8 would still be too close for me - I would cut them a bit larger and square them up and trim them before assembling the rows.
Hope it helps