A good rule of thumb on where to place the needle valve would be to use the shortest fuel line needed to get the fuel from the tank to the engine. For metal tanks and with an inverted engine, that would normally dictate that the needle valve would be to the inside of the circle. For some plastic tanks, with the plug holding the fuel lines near the center of the tank, needle valve placement does not make much different, then the dictating factor would be to locate the needle valve opposite of the exhaust/muffler.
Keith