When the ward mission fund balance gets large, try printing a detailed report of the donations to your ward mission fund. Make sure that there aren't any $400 donations in there that should have been credited to a specific missionary instead of the plain, ward mission fund. Also, your Bishop should be aware of why a missionary's individual fund is $1,600 down and whether the missionary's family needs assistance. You can point out the shortfall but the Bishop should find out why.
What if the reason is that four donations for $400 each were mistakenly put into the ward fund rather than the specific missionary's fund? Or maybe an uncle from another state donated $100 a month for 16 months but nobody recognized the connection to the specific misionary so it was placed in the plain Ward Mission fund? Patterns like that might be easy to spot in a detailed income/expense report.
My real name is Greg Anderson.