When pronouncing the letter "Dhaad" with kasra like "fil arDi" in Surah 59 ayaah 1 ....

Question
Title: The letter Dhaad

Assalaamu aleikum
You mentioned that the letter "Dhaad" is pronounced using the posterior 2/3 of the side of the tongue. My question is:
When pronouncing the letter "Dhaad" with kasra like "fil arDi" in Surah 59 ayaah 1 is the kasra sound in "arDi" pronounced from the sides of the tongue as well?
Jazaakalahu khairan
Wa salaamu aleikum
Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh
The articulation point is the same for the with any vowel or a sukoon.  With a kasrah the articulation point is used and the same time with retract our jaw for the kasrah.  The same procedure occurs with with a fathah, only the mouth is opened, and the with a dhammah, with a circling of the lips. 
 One can practice- if they pronounce the correctly with a particular vowel- then practice saying the with the vowel which is correct, for example with a fathah, then say it with a kasrah, then with a dhaamah being sure not to change the articulation point with each vowel. 
Wa iyyaakum.
Wa assalaam alaikum wa rahmatullahi wa barakaatuh