Area spells effect a square area. Casters have the option of reducing the affected area by concentrating the power of the spell more tightly. They gain an extra die in their pool for the attack by doing this.
For example if you have a spell of Flame(A3). The (A3) denotes that the spell can cover a 3×3 area. You have the option of concentrating the force of the burst to a smaller square, like 2×2. Add one die to the dice pool for each reduction in size.
Conversely, The caster may choose to boost the size of the area at a cost of 2 dice subtracted from the dice pool to attenuate the spell over a distance greater than it is designed for. This becomes more viable as the Character matures and grows a larger dice pool.