I'd like to suggest an experiment.

Take a piece of cord, and size, and tie it lightly around the middle of your thighs, around your sleeping bag so that it pulls the bag lightly to your body and see if in ten minutes your are not warmer. A better way is a 1/16" diameter elastic cord sewn just inside the inner cover of the sleeping bag so the nylon liner is held next to you, thus stopping drafts. By putting two of these in my WM bag One below the knee and one just below my hip joint), it became a warm wonderful bag with the ability to expand in most any direction that I want to push and I can wear what ever I want inside it and it always is the right size.
Jim
P.S. balaclava for wearing inside bag AND a pair of fleece gloves kept strictly for the sleeping bag.