Repeatability of eye placement is the goal, "Nose To Charging Handle" is a cute way for people to do it without needing to understand why they're doing what they're doing. You could have a chin weld and be fine, as long as the same spot on your chin hits the same spot on your stock every single time.
Red dots actually make this less important. The lack of parallax means that no matter where your eyes are, the dot is where the bullets are going to go. Every dot I've used had more parallax out towards the edges of the lens, but anywhere towards the middle 50% of the sight was good to go. Irons and magnified optics require more precise and repeatable head placement.
"Good judgement comes from experience, and experience comes from bad judgement"
If you've ever seen all those rubberbands, rigger bands, etc. on folks stocks, that's what that's all about (unless they're banding tourniquets on there). Get your stock to the proper length for you, using a felt tipped paint pen mark that spot on your stock, slap a parachute riggers rubberband on your stock and now you have a good, tactile reference point you can feel in the dark without even thinking about it.
This is not my idea, it's what was revealed to me during training and that dude was a DEVGRU/Team Six guy whose only advice that I got burned on was going heavy quad pic rail instead of the nice, newer lightweight options out there.
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