...he makes uke ...
So it is tori who makes rolling possible by executing the throw in a certain shape?
If I get this right, and we agree: Tori allways has the choice to throw in a way so uke can roll out of the technique.
My point was that tori can also decide to throw in a way that uke has no chance to roll.
... reach for the ground with one of his hand and began to roll over uke and to the mat.
Again, if I get you right I know this was of executing koshi nage.
But we use to hold the hand, uke could use to reach for the ground. It's the same like in kote gaeshi or shiho nage. And we try to "turn uke on the spot" instead of moving over/around the hips. So his back allready shows downward when he is falling.
I don' think that this is the only way to throw koshi nage or should be. That's really not my point. I just want to say, that aikidō teaches a lot of possibilities to throw uke, so he can not roll out of then technique on his own decision.
What do you think?