But I dont understand why you could not "knee-edge" if you dont tip your feet! Maybe I dont know what knee edging is. Im imagining its "pointing" your knee in some direction. Also, what is the difference between foot and ancle movements? Are not all movements of the foot done at the ancle joint?
Knee angulation, or knee edging, is basically rotating the femur so that the lower leg and knee points to the inside. Unless you do something with your foot this will also rotate the foot in the same direction so you have to point the foot in the counter direction, in relation to the lower leg. In relation to the snow the foot is still pointing the same way. Now since you cannot separate tipping and rotation due to how the subtalar joint is constructed (see the picture I submitted above), that means you HAVE to tip you foot. If you cannot tip your foot, you cannot knee angulation, except the small amount due to knee drive.
The ankle joint is the one responsible for dorsi and plantar. However, when you tip the foot the ancle itself moves side to side, maybe that was the confusion.
The foot has many joints, of which the ankle and subtalar are the most important for skiing. I suppose in layman terms the "ancle" can be used to represent several joint.