In my understanding it is more about "connect" than "harmonize". When I have worked with seniors at the Shiseikan, and in particular Inaba sensei, at any stage I feel he is "in control" of our encounter or at the very least connected with me and knows viscerally what is happening in my body/mind - indeed I sometimes have the impression he has a force field that encompasses everyone on the mat!
Certainly things to aspire to, and maybe I am starting to get an inkling of what it is about - my timing has certainly improved recently...
At the risk of opening a giant can of worms - I would say that (IMO) it's neither connecting nor harmonizing, nor much else involving what the other person is doing - including timing.
As I said, a can of worms....
Here's a relevant quote from Koichi Tohei, from "Ki no Kakuritsu" ("The Establishment of Ki").
The second Doshu interpreted Aikido as "the Way of fitting in with another person's Ki". However, it seems to me that Aikido is "Uniting body and mind and becoming one with heaven and earth. Specifically, the Way of fitting together the Ki of heaven and earth.".
Tohei's thinking is getting close to what I'm talking about.
In the section containing the quote above he was discussing his departure from the Aikikai, and his fundamental differences with Kisshomaru about what Aikido involves.