This much from my personal experience, which, as you rightly say, is a very individual matter:-
I received my attunements hands-on. I was repeatedly the only one who "felt nothing". I seemed to have no sense of the energy flowing, even when people whom I was treating said they felt a strong flow coming through my hands. I continued to experience nothing.
Through all levels of initiation, and after long periods of energy work, I felt ... precisely nothing.
The first time I felt anything was at the Saura site on "Reiki Revolution". A slight out of body experience.
I have recently visited James' Distance Reiju webpage, and given it a try out of curiosity, to see what might be learnt. I used the photograph as an aid to concentration, not thinking of it necessarily as a channel. But I did ask Usui Sensei to act as my guide in the process of deepening my connection with the universal energy source.
Well, I must say it "happened" for me. The earth moved. I was surprised to feel a great heat at the base of my spine, and a distinct feeling of floating, which I took to be the raised vibration of my energy body being temporarily out of musical harmony with the lower vibration of my physical body. This took a few minutes to readjust itself. I spent a long time over this, as it felt so good I didn't want it to stop.
I'm grateful for this experience, and hope to experience it again on returning to the Distance Reiju page from time to time.
Thanks, James.
Namaste!
firebird