In close proximity? What do you mean exactly?
If it's a distance problem then your ability doesn't have enough Cast Range. Otherwise, the AI behavior to cast the spell, assuming that's what you're talking about, is hardcoded to use a limited distance.
Another factor in casting spells quickly is a unit's Art - Cast Point field which acts similar to Casting Time. It delays the spell execution by the given amount of time to allow the casting animation to sync up with the launching of the spell effects. Unit's also have Art - Cast Backswing, which is the duration of time the unit spends returning to it's "stand" animation after successfully casting a spell. Set both of these to 0.00 for near instant spellcasting.
The settings I use to get a unit to cast spells immediately:
Art - Cast Point = 0.00, Art - Cast Backswing = 0.00, Movement Type = None, Speed Base = 0.
For a proper Dummy unit that has no issues casting spells:
Copy and paste the Undead/Locust, Set Model = None, Shadow = None, Attacks Enabled = None, Movement Type = None, Speed Base = 0. Then you can tweak some of it's Art settings to ensure there isn't any weird rotation problems. You can also use a custom Dummy model (look up Vexorians) to get access to attachment points which will help certain abilities display their Art effects properly.
