As far as i understand, the more corners you have covered the better, especially if you have an awkward shaped room like it looks as though you have.
check out this website:
http://www.realtraps.com/placing_mt.htm
its to a professional standard but theres quite a few helpful tips, really helped with my dissertation.
If you really want to take it further in perfecting your room follow this guide on how to measure your room:
http://www.realtraps.com/art_measuring.htm
and just in general these articles can be handy:
http://www.realtraps.com/articles.htm
if you check out some websites that offer professional treatment they sometimes have guides and videos
Niceone on the purchase by the way, always wanted a basement studio.