Gallows Island

[Bluetoes101]

Of the two proposed options for f/p I don't think either can be correct without "extra steps". 

"f/p" seem unlikely to be fancy "k/t". This is because of the lack of proceeding "e"
"f/p" seem unlikely to be "ke/te" ligatures for the same reason - the lack of proceeding "e" (kee/tee)

Extra steps example
"kee" in "p = ke" logic might be resolved by "cph". This would mean "ch" ends "e", the start would make new problems in this theory. 

This example is just what seems the easiest guess to me, but others may have better.