I heard the idgham of Taa into taa is naqis (incomplete) such as in the words ahaTtu, and basaTta

Question
Assalamu alaikum

A question on idgham al mutajanisayn (Hafs an Asim): I couldn't find this on your website, but i heard the idgham of Taa into taa is naqis (incomplete) such as in the words ahaTtu, and basaTta is this indeed the case and what category of idgham does it fall under (please give me a lesson reference as I couldn't find it)?

jazakumullahu khayraa
was salam

Answer
Wa alaikum assalaam wa rahmatullahi wa barakatuh,
Yes,  the idghaam is incomplete when a saakinah meets a voweled and the characteristic of   remains from the  .  In actuality, what happens is that the tip of the tongue from the top side collides with the area above the gumline (where the teeth meet the gum) with the characteristics of the , then separates from the same area with the characteristics of the .  The and share the same articulation point, thus they are mutajaanisayn. 
The lesson does exist on the old part of the site.  Unfortunately there was an error when the new site was designed and two the of idhgaam lessons were not included in the new area.   You can find it here:
http://www.abouttajweed.com/al-mutamathilayn_al-mutajaanisayn_4.htm
You will find that it does not mention the tongue colliding with the characteristics of the and separating with the characteristics of the , as this is new information we have been given by his emminence Sheikh Ayman Swayd and we can not edit the old part of the site anymore.  We will try and see a way to update the new site design to include these lessons and edit them, insha' Allah.

Wa iyyaakum,
Wa assalaam alaikum wa rahmatullahi wa barakatuh