Must I close my lip normally or i must open my lip a little for the ikhfa' shafawee?

Question
Assalaamualaikum.
I am not sure how to say ikhfa shafawi with the right tajweed,  must I close my lip normally or i must open my lip a little?

Wassalaamualaikum

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh. 
Much research has been done on this subject and his emminence Ash-Sheikh Dr. Ayman Swayd may Allah protect him, came to the conclusion that the lips should be closed. 
Please see the details of his research and related questions and answers at the following links:
http://www.abouttajweed.com/23070102.htm

http://www.abouttajweed.com/060602.htm

http://www.abouttajweed.com/kb/entry/67/

Wa alaikum assalaam wa rahmatullah.