What happens when the CG is too far back?

I build a foam plane(no name, scratch built) and originally felt that the CG was too far forward. Also, it seemed really twitchy but I think thats another issue with the amount of throw. Anyway I had to keep pulling back on the stick to keep it in the air.

I moved the CG back about 1/2" and introduced some dyhedral. At that point I was able to make two launch attempts before it crashed bad. It seemed tail heavy, I think. It would get about 20 feet away and leaned to the side and went down. Is that caracteristic of being tail heavy?

newman