Next time, more punctuation would help a lot. However, I think I understand your problem correctly...
The reason you can't shoot the same bps when you lower the MROF may be simple: "9.1 bps" doesn't mean the gun automatically allows you to shoot 9.1 balls in one second. It means the gun allows you to shoot once every 109.9 milliseconds. If you try to pull the trigger every 90 milliseconds, it will cancel every other trigger pull and the gun will not shoot as fast as you are pulling the trigger. However, if you then set the gun for 12.85, the board will allow you to fire the gun every 78 milliseconds. If you pull the trigger every 90 ms, the same rate as before, the gun will now register every trigger pull and shoot twice as fast.
In other words, if you pull the trigger faster than the gun allows it will cancel the shots. If you raise the ROF, you are raising the # of times the board will let you shoot in one second, and you can shoot higher bps with the same trigger pull rate. Does that make any sense?