Is it true that Ikhfa before letters with isti'la is different than before the letters of istifal. I have learned that the ikhfa before the letters of isti'la should also be pronounced with tafkhim.

Question
As-Salamu Alaykum

1. Is it true that Ikhfa bevor letters with isti'la is diffrent then before the letters of istifal. I have learned that the ikhfa befeor the lettes of isti'la should also be pronounced with tafkhim.

barakallahu fiekum

Answer

Wa alaikum assalaam wa rahmatullahi wa barakatuh.
Yes, during the ghunnah of the ikhfa', the mouth gets ready to say the next letter, so if the next letter has , the ghunnah will have tafkheem which will be clearly heard. 
Wa feekum Al-barakah.
Wa assalaam