, if everyone reading along will forgive us delving into some of the finer distinctions in this ...
I know not everyone has my flexibility, but if you do, the advice to "focus on sitting back as far as possible" can actually cause you to sit back _too_ far, turning your kettlebell deadlift into a squat. I know this from first-hand experience because, about six months ago at our 2017 StrongFirst annual leadership conference, I asked @Brett Jones
why I was able to set the bell further back than what I saw my colleagues around me doing, and he told me it was because I was squatting my deadlift. The give-away clue for most people would be their knees coming forward but I'm able to manage this while keeping my shins still very close to vertical. It's a cool stunt
but it makes my kettlebell deadlift worse, not better.
The cue I prefer is to push back into your hips as much as you can. If you can get your _hips_ further back, that's good, but getting the _kettlebell_ further back can also involve getting the hips too far down. I'm not sure it's just flexibility - I think it's strong hip flexors that allow me to do this, and undoubtedly something about my limb lengths, weight distribution, and leverages, too.
I just did a little test, positioning my feet so that the back of my heels were just touching a line on the floor. My furtherest-back kettlebell deadlift found the handle completely and just behind the line; my best kettlebell deadlift in terms of pushing into my hips found the handle completely and just in _front_ of the line. That makes the difference in placement about the thickness of a kettlebell handle, which is about 1-1/2" for the 44 kg I was using. (I know that if I chose a lighter bell, I could set it down even further back.) It's an interesting, IMHO, distinction. In the squatty deadlift, my thighs were close to parallel to the ground, but in the better one, they were higher and my hips were higher.