The vowel exchange "a" to "o"

[Petrasti]

Consider, for example, only the first four lines of f2v.

First, I add the words from the folio, and then the words you find in the manuscript with the o/a or a/o substitution.

kooiin - koaiin
cheo - chea
pchor - pchar
otaiin - otoiin
dain - doin
chor - char
cho - cha
daiin - doiin
chody - chady
cheor - chear

Not all words are subject to the exchange, but too many to call it a coincidence. Therefore, the question is whether anyone has already looked into this topic more intensively?