This poem uses an EO-rhyme, which consists of certain words ending in EO and IO. I think these words probably ended in a rising diphthong, such as [əw], and therefore do not rhyme with other words ending in -o, which fall into the E rhyme.
It seems likely that the poet chose the EO-rhyme because it rhymed with the theme, but interestingly the author of the first weiqi poem I looked at chose an E rhyme, suggesting that tonio could have been pronounced in two different ways, perhaps as [tɔɲɔ] at some times, and [tɔɲəw] at others.
|Staatsbibliothek 11.22 (View Online)|
|yacin šanyan juwe siden,||Black and white, the two sides,|
|maka kimun binio,||I wonder, is there some enmity?|
|arga bodon unenggio,||Are the plans and calculations genuine?|
|etehe seme,||Suppose you win,|
|5||aibe bahambio,||what do you get?|
|galai afambi seci,||When you say you’re making an attacking move,|
|yala bucunuheo,||aren’t you actually fighting?|
|wara deribun sureo,||Is it wise to begin killing?|
|efin dabala,||It is only a game.|
|10||batai adalio.||Are you like enemies?|
bucunuheo. I don’t find this in my dictionaries. I initially read it as *bucenuheo, from *bucenumbi, “to die together,” but I agree with the feedback in the comments below that it is probably becunumbi, and I have updated my reading to reflect that.