Jason,
In Part 3 you say "when using the A or E - but never together" that you haven't been able to see a thread that holds it all together. Surely the use of the open 5 string and the lowered 8 string is the same as the same pair of notes two frets back, using A & F? In other words, you are finding the same pair of notes, but in a different place? If so, the thread that works for the first half of that video also works for the second half.
As an example, fret 6, A&F gives the tonic (G) on string 5 with the A pedal, and the major third (B) on string 4 or 8, raised by the F lever.
Ok, so also is fret 8, no A pedal, you still have G on string 5, and string 8 lowered from C down to B by the E lever. These two positions are "synonyms"!
It just goes to show there's no substitute for knowing where the notes can be found!
