Maybe part of it is in the title of your thread: conservative, understated ratings.
Have you measured the loft on these quilts? A review of the JRB No Sniv in BP light said it was a rare experience when they actually measured MORE loft than rated. My JRB MW def has maybe 1/2 to 1" more loft than advertised 4" ( measured flat on the ground, less actually on the hammock)
That much extra down loft can be significant.
My Speer PeaPod, again when laid out on the ground, has way more loft than it's 2.5" single layer rating (5" total top+bottom). Look at this picture after 4 years:
So is the loft on your quilts thicker than advertised? Still, to take a 40 quilt to 22 would require it to be a lot thicker than advertised. Might also be the other factors already mentioned.