they measure loft on the quilt just like any other bag company measures loft on a sleeping bag. just to clear up any misconceptions.
there is a general acceptance for temp ratings on loft, and id say 2.5" is pushing a 20° rating claim, but not significantly exaggerated. my 2¢
then again, i have a tq i made that is about 30% overfill and it has only 1.5" baffles, overstuffed to 2". the density of the down takes me down to 20° without worry.
I doubt, however that the Ultra has a 30% overfill