The placement of your scriptorum will determine when/where your hero will deploy. Generally it is best to place the scriptorum near the HQ. If the scriptorum is placed too far forward, it makes it easier to draw out the hero without taking turret fire. Once your hero is outside the circle of your base, he can easily be killed by enemy units or dominated beamers.
On the other hand, if you place the scriptorum too far back or off to the side, an attacker may be able to destroy a lot of your base (or all of it) without even engaging your hero.
As a rule of thumb, place your scriptorum in such a way that the outer circle is close to the perimeter of your base. This means your hero will come out to attack shortly after the enemy engages your buildings, and he will not easily wander outside the protection of your buildings. Using a hero with a longer range will also help them stay inside the protection of your buildings.