I can respond to that, because in my early days as an engineer I was working on this very subject. The duct is shaped to avoid direct view of the engine. This is one element. We have provisions for allowing the insertion of radar-absorbing material in the duct so we could further reduce the signature of the engine. We also have the mechanical provisions to insert a vane that would split the duct to further reduce the visibility of the front end.
On December 7th, 2010. See this statement in context.