Are you referring to how far you can sink the opponent's power and thus getting to a point where it will naturally return?
Hi Allan, I thought you meant in the original post that you are trying to bring it all the way to the ground, and then the ground does what it does-- it provides a counter-push "naturally" as you point out. So in other words, unless you've connected the opponent all the way to ground, you have nothing, right? In other words if you get your connection mucked up at the hip, can you do anything at all like aiki-age? (In such a case you may have point of contact all the way to dan tien connected, so maybe you have something there?)
BTW I think Dan meant how low can the point of contact (starting point) be before you cannot do aiki age anymore, in other words, the lower you get grabbed, the more conditioning you need in order to have a chance for an actively controllable "up" force. (yes?)