The ideal position is what Olympic weightlifters call the "power position." In this position, the legs are in position to exert maximal acceleration of the bar (or kettlebell). The glutes and hamstrings are "loaded" with tension, which increases potential energy, for greater, and more rapid force development. Think of it as the position you would put your body into to jump vertically. Unfortunately, for a lot of sedentary (or those with little sporting background), this is not always intuitive. It has to be coached.
Below, a client was finally able to learn how to get into the "power position" and properly perform the hip "snap." I always start with proper deadlifts and swings. However, even after getting those down, there is still a large learning curve to use the rapid hip extension to move the bells under control to the shoulders (the rack position).
The bottom line is that it takes practice to master the hip "snap" to lift kettlebells properly. Very few individuals can do this intuitively. Whenever a weight is in your hands your brain wants to use your arms, back, and shoulders to lift the weight. In order to lift properly (and perform the best) you need to learn to stabilize with your arms and torso, and use the hip "snap" to move the weights.