Jason,
Chances are the plane is a little tail heavy. However, you didn't mention where the elevator is positioned when you have full down trim dialed in. The answer to pleasant flight on these planes is a throttle. I was even able to land and taxi back to the flight line yesterday! Just as a rule of thumb on 1/2A aircraft. I usually design my own. I always make the aft end (cabin to rear) a stick structure. I also install the batteries (heavy) behind the firewall and the rest of the radio components as far forward in the radio compartment as possible. Just a rule of thumb.
Dick
1/2A Forever