Is there an extra elongation of the natural lengthening before madd 'Iwad 'an Tanween (subsitute lengthening)?

Question
AsSalaamu Alaikum wa Rahmatullah.
My question is in reference to a particular madd.  When I listen to many Qurraa', I hear that when they are reciting very slowly or in the style referred to as Mujawwad, there is and elongation that I have never learned of in my study of Tajweed.  This is where there is an Ayah thats ending with a fat-hatayn, before the madd 'Iwad 'an Tanween, they also elongate the Tabee'i that comes before it.  For instance, the first aayah of surah Al-Fath, one would recite: "Innaa fatah-naa laka fat-hammubeeeenaa"  or in surah Naba' : "wa khalaq-naakum azwaaaajaa"

Is there a reason why the madd before the 'Iwad is so long?
Is there a reason why the ba in mubeena is recited so long?

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh,
The natural lengthening ( ) and the substitute lengthening ( ) should be the same length, that of two vowel counts.  The timing of two vowel counts is based on the speed of their recitation, so if they are reading slowly each vowel is one count, and this is mulitplied by two to make the timing for the natural lengtheing and the substitute lengthening.  Another way to measure it is with the timing of the alif.  An alif equals two vowel counts.  This is the measure we should use for the counts of lenghtenings, not moving our fingers up and down, or counting with our fingers. 
In conclusion: The natural lengthening and the substitute lengthening  (), should be equal in length, that of two vowel counts of the reciters speed of reading.  The natural lengthening should not be elongated before the substitute lengthening to more than two vowel counts even if one is  leading the prayer and about to stop recitation during prayer for rukoo', the length of both these  lengthenings (mudood) should not be more than two vowel counts. 
Wa assalaam