Is [a] always [a]?

[MarcoP]

Still unsettled, for me, is the relationship between [ai(i)r] and [ai(i)n]. Are these equivalent?

By pure coincidence, just a few days ago, I create this small overview:

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Thank you, Rene!
It really seems that i almost always appears after the diagonal stroke of a and before another diagonal-stroke character (n r l m).

Similarly, e almost always appears before another c-like stroke (d y). It often follows the c-like chape of a bench or bench-gallows, but there is the exception that it can also follow the vertical shape of a gallows....
Since, as Koen wrote in the initial post, one way to look at a is as c + i, it can connect a c-sequence with an i-sequence.

You point out a "continuum" in the position of the curl in n and r, which is another intriguing phenomenon: The strings ending in "r" also visually resemble the strings ending in "n" and there are numerous places in the MS where some intermediate form exists and the reading is very difficult.