That said.

I have a similar Big Agnes bag. I use a Thermarest "light pro something" pad that's got the tapered shape. No problems. I had a roll of Reflectix laying around so I cut a chunk to fit the sleeve in the BA bag. It doesn't weigh enough to care about and adds a bit of about 3.5r insulation to the package. We're just now getting out of our record high temps for December so I can't really swear that it's the icing on the cake...or bag as it may be.