Master Lin says the lower abdomin, but don't try and bring the lower abdomin in and the upper out.
Just focus on contracting the lower abdomin during the inhalve. Then the lower abdomin moving out during the exhale.
This is different from typical abdomin breathing. It doesn't take long before it becomes natural. Just focus on it for a few breaths then trust to the intent that it will continue in this manner and focus on the other elements of the meditation.
You are perfection.
Iam2 
