I was wondering what is the best setup with a suppressor. What is considered the best gas system best barrel length for reduced blow back?

I know that there is a substantial increase in blow black when using a suppressor but it seems that some of my guns are worse than others. My 11.5" BCM upper, 16" BCM mid length and 20" rifle are tolerable but when using my BCM 14.5" mid length the gas blow back is more pronounced and is bothersome. I thought the mid lengths would have less blow back than the carbine length gas system. I dont mind the dirty uppers, lowers, and magazines when using a suppressor, its just the extreme amount of gas in my face with the 14.5". All others are tolerable with the gas in my face.