There is some significant Discussion on this in the Mature Discussion but all I will say is the Church's point of view. Generally the Church calls whom they want to preside regardless of office. For instance a SIMPLE example: an Elder may be called to be Branch President even if there is a High Priest in the congregation with higher office, so in other words in the selection of a calling it seems the Church does not first look to see who has the highest office. Additionally the Church does not see the office of Patriarch as one of presiding.