Hey Thebutcher!
On the first pie factory L=3, the level start with 3 fireballs spawning at the beginning. But throughout the level, another fireball will spawn, and a fifth one will spawn later. So at the end of every pie factory, there will always be a total of 5 fireballs. But on stage 3, the level starts with 3 fireballs, on stage 4, the level starts with 4 fireballs, and on stage 5+, the level starts always start with 5 fireballs!
If you have any more questions, feel free to ask!