The key to this is to understand what you are trying to accomplish, not the form you wish to display. The purpose of angulation is to enable you to balance against lateral forces by moving your center of mass laterally. If you are square to your skis you can only do this a little bit by bending your body sideways. The body doesn't like to bend that way. Likewise if you move your center of mass (torso and all that stuff) sideways (lateral to your direction of skis' travel) by lengthening and shortening your legs you will change your edge angle (and probably skid).
The body likes to fold at the tummy. If your pelvis and upper body are turned away from the skis' direction of travel (probably facing down the hill a bit) you can easily move some of the mass of your upper body laterally just by folding at the waist (tougher if you have a fat belly). Your upper body then is making quite an angle with respect to your legs hence the term angulation.
Does that make sense?
In my experience its pointless to keep telling someone to assume the pose. They just don't understand what they are looking at or how to achieve it.
Oddly enough its comparatively easy to teach this to someone who has never skied before. If the first turns they learn are turns in which the skis are flat, like a narrow gliding wedge they learn to turn the skis by leg rotation, turning each ski by turning the leg in its socket. Just the act of making a wedge involves turning the legs. Active guiding of both skis in a wedge turn involves turning both legs. They already are learning upper and lower body separation and probably achieving a little bit of counter in each turn.
How this carries over into advanced skiing is that the muscular act of turning the legs in their sockets, while it can no longer turn the skis because they are edged, the effect of that effort is to instead turn the pelvis, producing a countered position from which you can angulate.
The trick is to acquire this skill and the movements and not to leave it behind as you progress through that mid level of ski ability when angulation isn't really much needed.
Most of us leave it behind. Maybe we were told to ski in a more squared stance. Watch a skier competing on the World Cup, particularly in slalom and you will see that marked upper and lower body separation. Its done by turning (or attempting to turn) both legs simultaneously in their sockets.
I hope this helps.