What should be the correct position of the mouth when making 'ikhfaa of noon saakinah or tanween when preceded by a dhammah?

Question
Assalamu'alaykum

What should be the correct position of the mouth when making 'ikhfaa of noon saakinah or tanween when preceded by a dhammah? Is it correct to circle the lips for the dhammah and then bring them back to a neutral position for the noon so the mouth shape resembles that of a kind of smile or should one just focus on getting the tongue ready to pronounce the next letter?

JazakAllahu khairan

Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh
The ikhfa' is when we hide a saakin letter (no vowel) before a specific letter.  Since the saakin letter has no vowel, our mouth should not be in the shape of a particular vowel, but instead should be in a neutral position.  The vowel on the letter before the letter being hidden does not influence the mouth position.  The neutral position should not be one of a smile, but instead the mouth should be at rest with no excessive movements.  During the ikhfa', our mouth prepares to pronounce the next letter, but not the lips. 
Wa iyyaakum.
Wa assalaam alaikum