As I understand it, outside of Combustion with no Heating Up or Hot Streak, you're spamming Fireball. Eventually you get a Heating Up proc but it will happen during the next Fireball cast because the previous Fireball has to travel to the target. You then cast Fire Blast to convert it into a Hot Streak proc.
My question is do you cast Pyroblast immediately after finishing the Fireball cast or do you use Fire Blast late into the Fireball cast (to avoid losing the Hot Streak proc), and then start another Fireball and cast Pyroblast at the end of that one?
Essentially is it:
-Fireball->Fire Blast
-Insta Pyroblast
OR
-Fireball->late Fire Blast
-Fireball->Insta Pyroblast