at least two flow ratio controllers each coupling to one of {HEAD ~ the plurality} of {TAIL ~ gas outlet ports}, the flow ratio controller splitting the flow exiting each gas outlet port; and 
of
at least two flow ratio controllers each coupling to one of { HEAD ~ the plurality } of { TAIL ~ gas outlet ports } , the flow ratio controller splitting the flow exiting each gas outlet port ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH