Brake Line Distribution block port sizes are different

I am converting my 66 Dart to dual master cylinder & noticed that 1 port on the distribution block appears smaller than the other 2. Am I correct in assuming this would be the correct port to block off and use the other 2 for the front brake cylinders to insure the same amount of brake fluid goes to both cylinders?
What was the reasoning behind this difference ?more pressure to the rear?