To some extent, you can use the Use Materia skill to shape the final result of using materia. By increasing the number of charges used, you can alter the size and range of the effect. With the Use Materia skill, you can change the final result in the following ways. Feats can also change the way you use materia, but the basic ones are spelled out here, in effect name/charges used/result format:
Using spellshaping effects increases the use to a full-round action.
Basic Effect———No charges. Range: 25 feet +5 feet/2 caster levels.
Creates a ray that deals 1d6/caster level of damage.
Enlarge Effect:———1 charge
Increase the effect’s range (as Enlarge Spell)
Burst Effect:———2 charges
Changes the effect to a 10 foot burst
Widen Effect———3 charges
Doubles the area of effect (as Widen Spell)
For example, you have a Novice Fire Materia, and you want to make a Fireball like effect.
You would use one basic charge for the fire effect, an extra charge to make a burst effect, another charge for the enlarge effect, and an additional three charges for the widen effect. So you’ll be able to cast a Fireball, basically, with a 90 foot range and a 20 foot radius area of effect, for 6 charges.