What do you mean with "alone work" or "self training"?
Do you talk of solo movements like the people who train in IS/IP?
Or do you mean something else?
I'm not sure if I know what is "IS/IP"... IS I don't know what is for sure. IP would be "Internal Power"? I read this word in many threads here, but do not have a "clear" image of what this really is.
To me, the "alone work" (or self training) is, in fact, "solo" work.
Definitely includes training of movements, like tenkan and other base changes, posture, "live" relaxing, etc. While I don't believe that body mechanics are the central point in doing aiki, if you can't even control your body you will never be able to do aiki, because the physical expression of aiki is done with our body (even if we barely touch the other).
But the "solo work" must include other important aspects like the mind/spirit training, or, the way I like to call it, our "state of spirit".
It's the ability to truly clear our mind of the "bad feelings", like the need to impose a defeat to the other, that will open the gates of our sensitivity and the possibility to do aiki.
In my life, only ONCE, in a practicing, I was in this "state of spirit" (I don't know how I achieved it, by the way). The only way I could explain what was like is that I "feel it" like if all my partners, for about 1:30h, were moving in slow motion, and that they came to me with a BIG RED X saying: "put your hand here"...
I really feel what was going on. Was an amazing experience. I never felt so good in my live as in that day.
I'm trying to discover how to put myself in that way since them. I don't find the way, but I'm getting closer. And to train outside tatami is where I'm failing, by not doing it.
I know, for sure, that this "state of spirit" is something that you can't achieve only by "tatami training". It's necessary a "life effort" and must start out of the tatami, training the body and the mind/spirit.
So, I'm talking of solo movements and something else, that I really don't know if I could explain...