Rosemary,
Yes you are right, "ease" is the word I was looking for.
Actually, for the "S" shape, just because I'm me
, I would do it in 2 steps - On the inner of the first curve and leave a "tail" of bias, then rotate the work and do the same on the next curve. There might be a spot where the seam allowance makes a little bump, depending if you fold the "hem" over the first seam allowance or not.
Andrée