The general consensus is that a scale airplane should be balanced nose heavy to prevent tip stalls, etc. This is a very bad practice and actually makes the plane want to tip stall even worse!
A flying airplane is a balance somewhat like the tetter-totter. When the nose is heavy, the tail has to balance it out. A nose heavy plane wants to dive so the horizontal tail must balance it out. Unfortunately if you think about it, this means the horizontal must pull downwards to counterbalance the nose weight. And how does that happen? UP trim. And along with UP trim comes DRAG.
To keep this explanation simple- the wing thinks the airplane is a lot heavier than it really is. And we all know a heavy plane stalls at higher speeds.
You can get away nose heavy with a light weight plane, but when it comes to a heavy scale airplane you are better off balancing it in the middle or even farthest aft balance point that the manufacturer recommends.
Ken