Have you ever tried picking up your phone and calling him? I actually call my Team Leader, at least I think that's what he's called, and ask him the important questions 'cause my FM usually doesn't know jack.
Whether you are interested or not in the per diem, you need to print the page concerning this and contact your tax person. Everybody is different when filing your taxes and your tax advisor would definately be able to tell you which direction you need to go.