Yoma 35 - NEW - שם המפורש

The Rivash (219) states that when we say on Yom Kippur אנא השם and אנא בשם, that is the way it should be said and we should not say Hashem's name. His reasoning is that if we would say Hashem's name the way we pronounce it now, people might think that is the way the Kohen Gadol would recite in the Beis Hamikdash and that is incorrect for there he said Hashem's name with the שם המפורש. However he concludes that when he says לפני השם תטהרו, here he can say Hashem's name even though the Kohen Gadol said His name with the שם המפורש. There are those that disagree and hold that the minhag is to say השם and not Hashem's name here as well.

What is the logic of the Rivash to make this distinction?