Birkat Cohanim: Seeing Each Other

A cohen/priest does not need to see the congregants and they do not need to see him during birkat cohanim. Birkat cohanim is effective even if you are outside the synagogue when you hear it.  But if you are at the front of the synagogue such that you would be behind the cohanim when they turn to face the congregation and say the blessing, you should move far enough so the cohanim will be facing you during the blessing.