Preparatory Prayers
The position of the celebrant during these [preparatory] prayers is unusual, although it is found in the customs of Cluny and in the mediaeval use of Westminster Abbey. The priest stands on the gospel side of the sanctuary facing the seat (cathedra), and the deacon remains in his stall. At a private Mass, the server kneels on the opposite side to the priest, facing the middle or gospel corner of the altar.
-- Archdale King, Liturgies of the Religious Orders
