Le Lévitique 9:22 Halakha : Mishneh Torah, Prayer and the Priestly Blessing & Shulchan Arukh HaRav

Thus too, one individual is not to recite the blessings before the Shema while all listen and respond Amen, unless a quorum of ten is present. This is termed Poress al Shema (Cp. Targum to I Samuel 9:13). Nor is Kaddish recited, unless ten are present. Nor do the priests solemnly raise their hands (to recite the priestly benediction) unless ten are present, the priests being counted in the number. For every group of ten in Israel is called a Congregation, as it is said, "How long shall I bear with this evil congregation" (Numbers 14:27). Those alluded to here were ten, (the Spies)—Joshua and Caleb being excluded.

How is this rite performed outside the Temple? When the Reader of the congregation reaches the paragraph in the Amidah referring to the restoration of the ancient service and he utters the first word of that blessing beginning "Be pleased",^*The first of the last three blessings of the Amidah. all the priests in the synagogue leave their places, proceed to the platform in front of the ark, stand there, with their faces towards the ark and their backs towards the congregation, their fingers bent in their palms, till the Reader concludes the paragraph of thanksgiving.^*The second of these last three blessings. Then they turn their faces toward the congregation, straighten their fingers, raise their hands to a level with their shoulders and begin reciting, "May the Lord bless thee". The Reader prompts them, word by word, and they repeat, as it is said, "Say unto them", which means that they are to wait till he recites. When they have ended the first verse, all the people respond, "Amen". The Reader of the congregation prompts them in the second verse, word for word, which they repeat till they have ended the second verse, when all the people respond, "Amen". And so with the third verse.

At the time that the priests bless the people, they should not look at the people and not get themselves distracted. Rather their eyes should be down, like one standing in focused prayer. For behold they are praying that the Holy One, blessed be He, should bless all of the Jewish people. And the people receiving the blessing should also concentrate on the blessing, so their faces should be towards the priests, because of the reason that will be explained below. And they should not gaze at them so as not to get themselves distracted and, all the more so, should they not gaze at another place.
Hence it is the custom in many places to roll down the prayer shawl [tallit] over their faces and their hands so that they cannot gaze at the people, nor the people at them – not at their faces and not at their hands.
And in these provinces, they have followed the practice of rolling down the prayer shawl only over the faces so that they are unable to gaze, but their hands are outside of the prayer shawl so that they themselves are unable to gaze at their hands and not get themselves distracted. And the people also roll down the prayer shawl over their faces so that they be unable to gaze at the hands of the priests. And this is the more correct practice, since the raising of the priests’ palms is revealed, and their prayer shawls do not separate between their palms and the people. For this is the meaning of the verse: And Aaron lifted his hands toward the people, and he blessed them (Leviticus 9:22) – that there not be anything separating between him and the people. And they did not say, “Even an iron partition does not intervene between the Jewish people and their Father in Heaven (Sotah 38b:20) – as will be explained – except when there is [already] a congregation being blessed by the priests inside the synagogue. [Only] then is someone who is standing outside of the synagogue also blessed with them. However, ex post facto, this is not an impediment. As behold [in] a city that is all priests, all of them go up on the platform [to recite the blessing, even though they are not facing anyone], as will be explained. (However, the prayer shawl on the face of the people is subordinated to their body, like their other clothes, and does not separate.
And they only forbade gazing; but just looking is permissible. However, we follow the practice of being careful [not to do so].