@Goukan Well, it doesn't matter if you want to disregard "Nika" as 2.9. Luffy not being 5.6 but a second 1.10 ruins the theory all the same.
Also, it's obvious Kuma's bounty and anniversary all have the 29, since that's how his fruit is spelled.
As for Nika being 2.9, there's no direct number for "ka". You have "ku" or "kyu" for 9 and "ko" can mean either 5 (because it sounds like "go") or 9 (because 9 is also spelled "kokonutsu").
Goroawase isn't science, it's just pun, it just needs to sound a bit alike. "Kuja" was turned into 9.2 for Hancock's birthday, for instance, but try to find "ja" for 2 in any goroawase guide in the internet, for instance... I never found out the logic behind it, but I think it's because it's close to "ji", which is an alternate form of "ni" (2).
"Nika" is not a direct translation of "2.9", but it's close enough to "ku", "kyu" or "ko" to fit as a pun.
I once saw a famous japanese theorycrafter (Yuderon) link "5" to "me" because it sounds like "mei" which is "may", the 5th month. Should we argue with a native speaker that he's not following goroawase charts in foreign webpages?
(And others argue that "me" is "6" because it's similar to "mu")
Here are different goroawase guides for reference: