It looks like you have it right there in the pictures. I have seen very few planes that are ballanced anywhere other than from the leading edge along side the fuse. One example that is not was my old Ultimate Biplane. Adjust your battery now for ideal balance and you should be good to go. For future reference MOST ARF's will not need a lot of extra weight to ballance if you use the recomended engine and servos. You should be able to balance by moving the battery around. When you start playing with bigger engines than recomended then you will find problems like you originally described... say stuffing a Saito 150 in that Dago or something like that. Now for why I used bold ont the word "most" above. Some of the cheaper ARFs from less than a major manufacturer may have severe design flaws where balance was an afterthought.