There's no need to setback a powder board. They're already plenty setback.
Setting back other boards behind what the camber is really designed for causes the issues you're talking about. In my experience, those issues don't show up in powder, but make themselves well known as soon as you hit a groomer. IMO, it's a give and take. If it's a really deep day and that's all you've got, set it back and deal with the little bit of sketchiness on groomers between pow stashes. I also never set my bindings back beyond what my normal stance width would allow.
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