One thing you will notice when you go too wide is turn initiation especially for toe side starts to feel awkward and hesitant. I feel like my rear foot "hangs" when initiating the turn.
I've ducked out as far as my knees will let me, 15/-15 feels good.
I really noticed the hesitation in toe-side turn initiation in the deep powder last week. And then I flew back east and rode that night after an all-day freezing rain. Talk about culture shock! And that's when I felt trapped and unable to get lower over my edge.
I've narrowed my stance by an inch and I'll be riding later in the week. Really hoping I'll notice the difference.