《明史·志·卷三十二》
品级相近的行礼，便东西对立，位卑的在西面，位高的在东面。
品近者行礼，则东西对立，卑者西，高者东。
When the ranking was close, the salutes were performed by facing east and west, with the lower ranking person in the west and the more senior person in the east.