My question is about ikhfa shafawi and its' pronunciation by closing the lips. Would the action of closing the lips ?

Question
Assalamu 'alaikum wa rahmatullahi wa barakatuh

My question is about ikhfa shafawi and its' pronunciation by closing the lips.

Would the action of closing the lips be the same for ikhfaa shafawi and idgham sagheer mithlain? In some books I have read that the closing for ikhfaa is not as tight (with less pressure) as for the idgham. It is more of a touch the lips together rather than a firm and proper closing. Is this correct?

Is there a difference in sound between the ikhfa and idgham of the meem sakinah apart from the length of the ghunnah and the different letter that is read after? Should they both sound the same?

Jazakallahu khairan

Wassalamu 'alaikum wa rahmatullahi wa barakatuh

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh
The collision of the two lips for both the ikhfa' ash-shafawee and the idghaam mithlayn of the is the same.  There are some who say the collision of the two lips is lighter, but there is no distinction made in the early (old) books of tajweed.
The difference of sound between the two comes at the end of the ikhfa' and idghaam.  In the ikhfa' ash-shafawee, the sound starts with a and ends with a with its accompanying vowel, whereas in the idghaam mithlayn of the ,  the sounds starts with a and ends with a with its accompanying vowel.   During the ghunnah, the two sound the same, except for as pointed out in the questions, the ghunnah is slightly longer for the idghaam than the ikhfa'. 
Wa iyyaakum
Wa assalaam alaikum wa rahmatullahi wa barakaatuh