You said you have a friend "who knows". Ask him which passage or passages from the main gallery 1-4 are going to receive no flow because the gallery is being fed from opposing ends. Maybe he can explain why this happens.
How about I give you HIS number and YOU do it? You are straining at a camel to swallow a ******* gnat. If you want you can plumb 5 hoses there and you can turn 75K and rule the world.