The following is what I have drafted as a result of my pondering:
I served a mission in Japan following the crackdown on practices that led to baptism contests within and among missions, quick baptisms of people who were woefully unprepared (and, in some cases, not fully aware of what they were doing) and the inevitably horrible retention rates that followed. Thus, I am sensitive to the way "success" is defined in a mission and the pressures that missionaries can face with regard to goals and, ultimately, things that are outside their control. I understand and appreciate faith and trust in the Lord, but I also understand and honor agency as the foundational gift of mortality - right alongside and part of the Atonement itself.
My only request is that "success" be defined as it is in "Preach My Gospel". That manual is crystal clear that success is not measured by number of baptisms - or any other metric that involves the agency of others. I loved my mission and understand and support completely the need for measurements of missionaries' personal efforts, but I also have friends who had horrible experiences on missions due solely to high pressure sales tactics and success metrics used by their Mission Presidents and, as a result, their AP's and Zone Leaders.
I want people to be converted more than I want people to be baptized, and, again, I want success defined as it is in Preach My Gospel, not strictly numerically. I want missionaries to be faithful, successful missionaries, but I don't want them to feel like they failed if they end up having an Elijah mission and not an Ammon mission. I would love for each of them to have an Ammon mission, but I would be happy if each of them becomes an Elijah if that is what the Lord has in store for them.
There is nothing specific to you that makes me feel uneasy or concerned, so please accept this as nothing more than the desire of my heart for my own children and all others who serve missions. I appreciate deeply your and your wife's sacrifice and dedication in accepting the call to serve as Mission Presidents and in nurturing the missionaries. May God bless you in your own efforts, and may your success be measured in the same way the success of the missionaries you serve is measured - whether you look back and feel like Ammon or Elijah.