Jack had much to say, he covered everything I could think of, and then some. Specifically regarding the quilt-- 1) I was babying the quilt, afraid I was going to tear the baffles. The repeated vigorous, I think he said "almost violent" quilt shaking, really made a difference in the quilt lofting, which seemed to make the difference between the down packing into the edges of the quilt in the middle of the night versus staying put above me. 2) Body heat would help loft the quilt. 3) Partially unzip the bivy to prevent compression of the down. 4) Don't tuck the quilt under the body, this puts pressure on the quilt above me and compromises loft. Just let the quilt drape loosely over the body. 5) Properly adjusting the drawstring at the top of the quilt creates a "pocket" which tucks around the shoulders, helping to hold the quilt in place.
The first two nights I used the bivy partially unzipped, I had a lot of condensation inside the bivy while never feeling sweaty or overheated. I had little loft left above me a few hours into the night and ended up re-positioning the down around three times both nights. Temperatures were mild but I was still not comfortably warm in my Red Hot Chilis Pepper Skins, medium wool socks and fleece balaclava.
Third night I ditched the bivy and Prolite 3 and dug a hip hole ( Jacks suggestion for staying put at night ). This was a revelation. I have not slept comfortably on a blue pad in 15 years, but this time I was incredibly comfortable with a one inch deep hip hole under the pad. I definitely thrashed around less, slept mostly on my back, but still discovered absolutely zero loft over my hip in the middle of the night. I shook the down back towards the center of the quilt and went back to sleep. I was surprised to find plenty of loft above my hip when I awoke in the morning. Hmm.
The last night followed two warm nights where I occasionally felt sweaty, and I had not dried the bag in the sun a full half hour like I had done before my first "successful" night in the quilt. Down packed into the edges of the quilt in the middle of the night, and I was once again disheartened. I shook down back to the center and went back to sleep. Next morning all the baffles were still lofted in the center of the quilt, and I stayed under the bag for another two hours, getting in and out and generally moving around a lot. The quilt retained its loft in the center this whole time. In fact, the baffles were so puffed up they gave the impression that they were going to pop.
My theory is that loft was somewhat being defeated by moisture, and without enough loft pressure pushing against the nylon and baffles, the down has no resistance to sliding to the edges of the quilt just by gravity, and any extra help I could give it by moving around and pushing on the outside with a bivy. I have more testing to do but have had results which give me enough confidence to keep going with the following rules of thumb...
1) Make sure the quilt is absolutely dry!
2) Don't use a confining bivy which pushes against the down and defeats body moisture evaporation.
3) Shake the quilt. Really shake it. Wait 15 minutes. Do it again.