f and p appear predominantly in the first lines of paragraphs

[Searcher]

Searcher, that sounds fine at first sight, but it would mean that, ignoring paragraph markers and labels, P only occurs 63 times in the entire core text.

I could understand this if it represents a foreign sound or glyph, like Marco suggests, but with these statistics in mind it is not possible to map this gallow to a normal sound in a one-to-one substitution.

Yes, in this case I defend my theory that

k, p - c, g, q
t, f - p, b, m

but it must not necessary be quite this solution, it can be another pairs: k and f, t and p, or k and t, p and f, which may mean the same marker. I work with my own theory, but this and the other mentioned possibilities must be checked.