Depends on length of barrel, hole size, caliber, comp, load. At some point the holes will take away gas from allowing the comp to work most effective.
I have 4 on 5” 38 barrel with Akai gill comp
3 on 5” 9mm barrel with Akai gill comp
3 on 4.65” 38 barrel with Akai shoto comp
Also depends on what you want. There’s more to it than just flatness. Like dot movement, how hard it hits your hand, dot tracking, return to zero.
5” 38 barrel with 4 holes and gill comp tracks the best.
4.65” 38 barrel with 3 holes and shoto comp is the flattest, and fastest return to zero but hits the hardest.
Both are running AA#7 with 125gr BB