I have a habit lately out of experience to cancel a fireball that started casting if a !pyro was indicated on the screen momentarily before the fireball started casting, in order to get a bigger ignite for a combustion, if an ignite was already on the target. However, since it's so empirical and came out of common experience and I've never read it as a proper method by theorycrafters, I wonder if I miss something. Let me know what you think. By the way, I cancel the fireball often by moving half a yard front, clumsy I know:P