Adding down/feathers to a synthetic sleep bag?

[petedelisio]

Adding to an old cats meow. Trying to make about 0° comfort.
Any advice...

[petedelisio]

One particular question I have, is should I add the down and feathers across the top of the synthetic insulation or the bottom closer to me?
I probably won't add any to the backside (bottom against the ground, especially if the baffles are separated top and bottom