|Last week I noted while watching my brother-in-law ski that his stance was narrow at widest part of the turn and was wider as he hit the transition. Essentially he was skinny at the outside of the turn, kind of wide (V-ing even) at the middle (transition) of the turn and then narrow again for the apex of the next turn.
What you have described here is very likely a sign that your brother-in-law could use some work on the activity of his inside leg and ski. Here's what I believe is happening: In a turn, everything feels pulled to the outside, of course. If we stand exclusively on the outside ski and relax the inside leg, the inside ski will be pulled toward the outside ski, and the stance will narrow as you described. Then, as he reaches the end of the turn and the transition to the next, he starts thinking about the new outside ski, and activates it with some twisting that causes the widening stance and the little stem ("V").
The main problem with this lack of inside leg activity is that it often results in more skidding than he probably wants. That twist of the new outside ski in the transition starts it skidding. And when the inside ski gets too close to the outside ski, it gets in its way. Because the outside ski's tip can no longer carve into the turn, the only option remaining is to skid its tail OUT of the turn.
There are two possibilities for inside leg activity. One is to put some weight on it and tip it, so that it carves like the outside ski. This is the skill the Railroad Track exercise helps develop. When it carves, the snow pushes it through the turn--into the turn, AWAY from the outside ski.
If you remain 100% balanced on the outside ski, the snow will push IT into the turn, but something has to pull the INSIDE ski into the turn--and that means YOU. A ski, boot, and leg are pretty heavy--say, I don't know, 35 pounds? Imagine a 35 pound weight on the end of a rope, and you're swinging it around in a big circle. Think how hard you'd have to pull on that rope! That is how much effort you, as a skier, must exert to pull the unweighted inside ski through a turn. That's a lot of effort. Any less, and it slips out, interfering with the outside ski (as in your brother-in-law).
Real contemporary skiing sometimes involves pressure on both skis, sometimes on just one. Either way, you have DO something with the inside ski. As I've often said, "The outside ski may be where the action is, but the INSIDE ski is where the ACTIVITY is!"
In this way, skiing is similar to walking. You may stand on one foot at a time, but you have to MOVE the other one.
So your brother-in-law might try this: to initiate a turn, rather than transferring weight to the new outside ski and twisting its tail out, he should try to move the TIP of the INSIDE ski IN to the new turn, and continue that effort all the way through the turn. Note that is is not just a small change--it is the polar opposite of what he is doing now. Inside vs. outside, tip vs. tail, IN to the turn vs. OUT to a skid.... He will literally pull the inside ski AWAY from the outside ski, from start to finish. It need not actually move away--the stance need not actually widen--because the outside ski's carving effect will cause it to "chase" the inside ski. If everything is perfectly precise, the stance width will not vary--which may well answer your initial question!"Right tip right to go right"
This is the mantra I have repeated over and over in this forum, as the primary, essential move and thought of contemporary high-performance turns. It is an applicable thought whether you keep that new inside ski weighted as you enter the turn (as in railroad turns) or you transfer your weight to the outside ski. There is obviously more to the movement than the simple words suggest--clearly, you have to release the edge of the downhill ski before you can steer it into the new turn. But "right tip right to go rght" is really all you have to THINK about to make these things happen (in a right turn, anyway).
We've had many great discussions here at EpicSki regarding stance width, weight transfer, inside leg activity, and steering--all issues closely related to your question. If you have some time, search through the archives for those terms. Happy reading!