In free skiing, and building up to these big angles I think getting the inside foot out from under the hips so that both skis are on the same edge angle is important. I see it often that the outside ski goes out on a good angle but the inside ski stays flatter and under the body, limiting speed and grip - almost like doing a pistol squat but with the extended leg to the side rather than out front. Getting the feeling of both feet outside the torso in the turn is helpful I think.
Very true, and this is helped by having a narrow stance, instead of wide and using the inside ski as an outrigger.
^^^
I think you guys are talking about an effect, not a cause. If you move inside too early / too bank-y / without a well-engaged tip, you're going to end up with this kind of stance, right?
It's a matter of balance on the outside ski and the ability to commit to the outside ski. Lacking balance will lead to inside ski being used for either weight or balance (put under the hips, even unweighted).
Leaning inside is most often resulting on weight on the inside ski - the skier can't commit to the outside ski. But a skier that can lean outside a lot can also have the commitment issues and ends up way too wide, with the inside ski under the hips... especially hip dumpers, since their balance is impaired by using the big muscles. Tippers tend to stay narrow as they have good foot control.
That's why a narrow stance (or vertical separation at big angles, like in my avatar) is generally preferred - it's so funny to go to a course and see the course conductor ski wide only those 3 turns when he says we should ski hip-width, but ski very narrow the rest of the course.
... your skiing can fall apart even when you're having a bad day - that's not something you'll normally see, as most skiers wouldn't publicize the bad day skiing, but as a community service, here's "a friend" having a bad day:
Absolute weird snow, you can see little commitment to the outside ski, way back on the skis and rotating as a result and a hugely big wide stance (given how he normally skis) with the inside ski opening up way early, especially on the pitch. In one word: big commitment issues... and survival instincts kicking in...