Peter A Goldsbury
If uke remains firmly anchored to the ground, then the waza becomes very difficult, if not impossible.
Best wishes to all,
That is very important remark, and is valid for all techniques in aikido.
The right way of doing techniques comes not from pictures, some esoteric explanations or opinons expressed in conversations, but from correct using of biomechanic of human body.
So the question is, how, in koshinage, one unroot uke from the ground to put him on the toes AND preserve this state until he fall down - using one hand? one wrist? It is simply not possible unless uke is jumping by himself.
One must use his WHOLE body, in preference, legs and hips, that contains the biggest muscles. This is only possible when one use horizontal and vertical dimention of movement. With legs apart such most effectif way of using human body is impossible.