Rocket,
I like your analysis. If x = .1 then the down has a bit more pressure against the fabric to keep it from deforming under slight pressure, such as a rain shell or wind pressure. As an aside I have noticed that down insulators that flap in the wind lose a great deal of their warm and "indoor measured loft". When you say "normal" are you saying "at the maximum limit of expansion vs the available space inside the garment?" I think that's what you are saying and this is specifically my problem with ultralight garments and I'm not sure that "over-stuffing" enough to prevent deformation by slight pressure should be referred to as "overstuffed, but rather "correctly stuffed". I think the industry is playing too much on the numbers and peoples desire for minimum weight to want to do this, it also costs a bit more expensive down, but heaven forbid that they lose sales because their "improved loft" model weighs 1 ounce more.


One big difference between my Wm Kodiak and a Wm Puma which is rated far lower, is one vs two draft tubes. My back was decided cold when sleeping with my back against the zipper. I took the bag back to WM because I felt it didn't hit its rated value because of this and they put more down into the draft tube, a couple of ounces, enough to add a bit of weight, but also a lot of warmth.

As another aside, the bag is huge, designed for a 250 pound 6 foot 6 linebacker and I'm a little guy who likes to be able to stretch out in my sleeping bag, so I inserted 1/8" diameter elastic inside the bag just under the inner liner, above the knees and near my waist. The bag is a lot warmer because of this. It both isolates three area in the bag lowering any internal drafts to zero AND it bunches the bag up giving more loft, AND I can easily stretch in any direction and then the bag always snuggles up to me. This bag is rated at -5 and would be pretty comfortable at -5, but if I pull my big down coat over it, I am actually warm and toasty at -5. The bag has enough "resistance to compression from outside influence" that the coat does not cause its loft to suffer.
Jim
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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.