If the hammock is narrower than 150cm, and the sides are low, it will drape over you as opposed to be suspended above you. That makes it work better in terms of staying warm.
If your hammock is wider than 150cm, you can hang it with more sag and get the same effect in a pinch. It may not be as comfortable, but it will be warmer.
Plugging the air gaps in the ends with any loose items will also reduce the amount of volume that your body is heating, which in term keeps you warmer.
The peapod has all kinds of ways to be used for extra warmth than the stated rating.