The gemara says that one should be careful to annunciate each word in kriat shma.
Why Hakanaf P'Til and Eisev Bsadecha? It's a phay followed by a pay and vais followed by a bais, which aren't the same sound.
I saw A Daf A Day discusses it. The answer we gave in shiur this morning was that there are different ways to pronounce vais, and sefardim read it as bais. For example they say Rav Obadia Yosef (the maggid shiur said he knew this to be true among Iranians specifically)