I generally roll my bag up and stuff it (without a stuff sack) into the bottom of the pack, then everything else goes on top. As mentioned above, it fills the shape of the pack far better that way than it would if using a stuff sack.
As to Stephenson Warmlite, I tend to ignore/read with a grain of salt most anything they say... The tone of their website (and the chain of letters posted here) are enough to push me away from them. They definitely had some innovative ideas (incorporating the pad directly into the bag, for example) a few decades ago, but they've long since been surpassed by other companies and have failed to do any further innovation of their own.