Sorry for the late reply, I also don't check the forums much.
My initial comment was just a note that it looked like you got mixed up by the spacing of the furigana and thought it was two different furigana comments (Baku + Rusu) instead of one (Bakurusu).
But yes, furigana as alternative reading comes up from time to time.
Honestly I often forget whether the big words are the "real" reading or small words are "real" reading so maybe just do whatever makes more sense.
I think in this case, the author did it to show that what the knight actually said when using his ring was "Baculus!", but by itself this doesn't mean shit to us readers so the author added the proper reading of "the power of a ring" alongside that to clarify.
How you integrate the added info of the furigana is really up to the scanlator.
Some people work it into their translation directly, some people just add tiny English text on top of the words, some people just add a TL note at the end of the chapter...
I think it reads fine as "the power of a ring", anyways.
Here's some more discussion on the use of furigana/ruby characters as alternative readings/contextual information.
https://community.wanikani.com/t/furigana-in-mangas/58552/2
(I really appreciate you commenting, btw, I just don't read the forums that often, except for - mostly - right when I upload. Just in case I seem to be slow to reply!)
You might need to explain that a bit more for me to properly get it - are you saying it's basically supposed to be read like "the power of a ring" (or whatever a proper translation would be) and "Baculus" as a separate thing together, rather than the furigana being a guide? I'll take your word for it given you know the language waaay more than I do, plus I can see how that would make sense given the way the fight is structured/the panels are set up, but I was unaware you could use furigana that way.