The mixing, blending, combining? These words may well have been used in certain arts in the past and even today but they are not the terms mostly used by O'Sensei and thus his meaning for AI KI or even Ki.
He most usually used the words harmonizing, harmonizes.
Wait, wait. The fact is he didn't use "harmonizing" or "harmonizes" at all! He used Japanese words, and you are talking about somebody's translations of that. Plus he used religious terminology. And he used references to the ancient literature. It is questionable for those of us who don't speak Japanese to say that "harmonize" is the correct translation and mix, blend, or combine are incorrect. But beyond the language issue, there is still far from a "correct answer" due to the strange terminology he used.
I don't want to put words in O-sensei's mouth. I don't have any agenda. But I really think we have a lot of work to do regarding understanding what he meant. So we do need to have these conversations. And we need to trace the kind of things that he said through a lot of mess in order to arrive at good translations.
Looking at the traditional meanings of neijin-related terms that O-sensei would have read is a good way to do it, and the cultural, historical, and religious analysis that people like Peter Goldsbury, Stan Pranin, and Ellis Amdur do is also an important and necessary task.