738. After Duchening

100:13 While the kohanim are reciting the blessing, the congregation should not say any verses; they should just listen carefully and pay attention to the words of the kohanim. It’s worthless to be blessed and not to pay attention to the blessing, and if someone is reciting verses, he can’t be paying attention. Nevertheless, some have the custom to recite verses and they should be careful only to say them while the shliach tzibbur or the kohanim are singing, not when the kohanim are saying the words.

100:14
After duchening, the shliach tzibbur starts the bracha “Sim Shalom.” At this point, the kohanim turn back to face the aron in the east and they recite the prayer “Ribon Ha’olamim…” (“Master of the universe…”). They prolong this prayer until the shliach tzibbur finishes the bracha so that the congregation will be responding Amen to their prayer as well. If they can’t prolong the prayer that much, they can add “Adir bamarom” (“Mighty One above…”). On Rosh Hashana and Yom Kippur when they sing “Hayom t’amtzeinu” (“Today we strived…”), the kohanim should not start to say Ribon Ha’olamim…” until near the end so that they may finish together with the shliach tzibbur.