Not picking on Steve here at all, because I inadvertently made the same mistake in my wording, but for the sake of accuracy in terminology...
A down quilt is divided into chambers. The maximum height of the chamber, which vendors list in their specifications as loft height, is shown on this graphic as Hc. The chambers are separated by strips of mesh sewn between the inner and outer shells, which are called baffles. The height of the baffles are shown on this graphic as Hb.
What gets a little dicey with a differential cut underquilt, is that as it's suspended from the hammock and curves to fit the occupant, the differential cut allows the outer shell to expand more than the inner shell, such that Hc and Hb become closer to being equal. However, I still believe most vendors are probably specifying loft height (Hc) with the quilt laying flat on a table. That's how it's always shown in photographs when there is a ruler held up against the quilt.
Graphics extracted from the CatSplat Differential Underquilt Calculator.
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