Do you have the sintered rotor version?
I run at 2 different tracks. One is real high bite and tight. I run a 16t on a monster and a 21t on the sintered 13.5 in the t4.
On the other track I run it is semi high bite and a little bigger. I run a 17-18t on a monster and 22-23t on a sintered 13.5.
I also run the original 13.5 in my b4. On the tight track I would run a 19t on a monster and a 23 on the original 13.5.
I don't run much 19t so I can't help you there. Its either 13.5 stock or brushless mod.