Re: Koshi Nage
It is a mistake to be preoccupied with the name of the throw, because, functionally, "nage" is deceptive. Properly executed, one does not "throw." Were one to use a name that describes what one does, it is "koshi-kake." (Hip-trip). In whatever position you have your feet, you establish kuzushi (uke is forward weighted on the balls of the feet), and you position your hips at a point right above his knees. The effect should be the same as if, unawares, one walked into a tightly stretched rope at that height. In classic aikido, the hips are perpendicular to the uke. Finally, it is very important to maintain your hip height until uke goes over. If you start to stand up, or heave him on your hips, you will actually restore his balance (unless he's a dive bunny). The same is true for judo's ogoshi, btw.