TGU Press to Elbow

I have Kettlebells From the Ground Up and am really liking it, but there are still a few technique questions I have regarding the TGU.

The one I would like to iron out now is the Press to Elbow.

1. When performing the Press to Elbow, where should most of my power come from? I can see from the video that the motion begins by rolling further onto the side of the straight leg. From there, should it feel more like a sit-up, with the power coming from the hip flexor and the abdomen area, or should I think of turning my hips like swinging a bat or throwing a punch and having my upper body catch up to my hips? How much power should I get from the foot of my bent leg? Should I flex both glutes as hard as possible? How much assistance should I get from my down elbow? It amazes me how some people do this with seemingly little effort.

2. Should the bent knee remain pointing up so that there is an angle between both legs? I notice that when Brett does a TGU with 48 kg that he allows the bent knee to point more in the direction of the down leg, but maybe that is because it is 48 kg. Would perfect form keep the bent knee pointing up with the hips more open?

3. Should the straight leg remain straight with the toes pointing up, or is a little movement desirable here. Again, when Brett does a TGU with 48 kg, the down leg bends and the heel is drawn towards the hips.

I do not mean to nitpick at all, I realize that 48 kg is a lot. I am just trying as much as possible to dial in perfect form and want to know EXACTLY what I should shoot for.

Thanks,

Jeff