If you're narrower than Reilly, then you got a problem...if not however, then you're too wide:
this:
they're all level 4s, but JF is a sometimes wider, which is likely the reason for a visible A-frame.
The reason you can't get narrower is lack of balance, that's why skiing with a narrower stance is important, to build balance on the outside ski. When you "fall into a turn", you don't want to think of supporting with the inside foot - this is why most people keep it wider than needed. Instead you want to think just balancing on the outside ski throughout.
1. on dryland, develop one footed balance. use a bosu ball, a balance board or any other devices you can think of and spend time balancing on one foot
2. there is a specific drill you can do on dryland: put a cloth / towel on a flat shiny (slippery) hardwood floor. stand on it with the feet one foot apart. Then
pull both feet together. This will develop some muscles seldom used outside of skiing. Warning: it is quite painfull in the beginning... but keeping your feet together does require conscious effort in the beginning.
3. on snow, the most important is to ski on one ski only. Lift the other heel of the snow and keep it close.
Here's JF - you can see he naturally narrowed the stance when standing on one ski only (as you remove weight off the inside foot, it's unnatural for it to stay far and wide - that would also change the alignment of the body, to compensate):
Then, after a few turns on one ski, with the inside heel lifted, start skiing with both skis on snow, but still weighting only the outside ski and paying attention to the stance.
The classic view on stance is that it should adapt to what you're doing. If you're doing a speed run over bumpy terrain at low edge angles, go wider, which tends to be more stable. Otherwise, a narrow stance provides the required mobility, as you want to be mostly on one foot anyways.
cheers