Method of Salaah

Folding one's hands after ruku when praying behind a imaam who reads longer zikr than ''Rabbana lakal hamd''

Q: Must a Hanafi fold his hands after ruku when he prays behind a imaam who does longer zikr than ''Rabbana lakal hamd'' such as;

رَبَّنا وَلَكَ الحَمْدُ حَمْداً كَثيراً طَيِّباً مُبارَكاً فيه

Rabbana wa laka l-h'amd, h'amdan kathiran tayyiban mubaarakan fih

Changing a letter during recitation in salaah

Q: I read in a book that if you change a letter during recitation in salaah, the salaah is broken. Such as reading the letter ت instead of  د such as at the end of Surah al Falaq reading HASET instead of HASED. But somehow when I recite HASED no matter how much I pay attention to recite it with D I hear a T sound at the end coming out. Does this still break salaah? To break salaah does it need to change meaning, if HASED is read as HASET does it change meaning?

Surah Faatiha in the 3rd and 4th rakaat

Q: I want to ask whether I have understood a masalah correctly: In a book it was stated that according to some Hanafi ulama reading Fatiha in the 3th and 4th rakat is Sunnah, and according to some Hanafi ulama it is Wajib.

Then the book stated if Fatiha is read twice in the 3th and 4th rakat, there no sajdah sahw by ittifaaq.

Do I understand correctly that sajdah sahw is not due by ittifaaq because whether Fatiha is Sunnah or Wajib in the 3th and 4th rakat, it is not Wajib or Fard to go to ruku after recitation of Fatiha in the 3h and 4th rakat and it is permissible to read more, but since it is permissible and not Wajib or Fard, there is no delay for the ruku, hence by ittifaaq there is no sajdah sahw due if someone reads Fatiha twice in the 3rd and 4th rakaat, whether reading Fatiha in the 3th and 4th rakaat is Sunnah or Wajib.

But in the 1st and 2nd since it is Wajib to read a surah after Fatiha one would delay this Wajib if one was about to read Fatiha twice hence sajdah sahw is due because of delay. But if one reads in the 1st and 2nd rakat first Fatiha then a surah then Fatiha again then there is no sajdah sahw because going to the ruku after the surah is not Wajib or Fard and it is permissible to read another surah after surah. Hence no delay thus no sajdah sahw.

Did I understand this masalah correctly?