Deacons at Sunday Celebrations in the Absence of a Priest

A permanent deacon assigned to our parish and I differ on his use of the presidential chair during Sunday Celebrations in the Absence of a Priest. Would you please clarify this issue for us?

A deacon, when one is available, is the appropriate leader of a Sunday celebration in the absence of a Priest, because the deacon "is called in a special way to lead these Sunday assemblies." (Sunday Celebrations in the Absence of a Priest [SCAP], number 19).  "Since the deacon has been ordained for the nurture and increase of the people of God, it belongs to him to lead the prayers, to proclaim the gospel, to preach the homily, and to give Holy Communion." (SCAP, number 19).

Regarding the use of the presidential chair by a deacon during Sunday Celebrations in the Absence of a Priest, number 24 of that ritual states: "Leaving the priest's chair vacant, he uses a chair other than the priest's as a symbol that the community awaits the presence of the priest."