In {TAIL ~ a further arrangement}, the combined cross sectional area is less than 20% of the cross sectional area of {HEAD ~ the hollow interior} 
In { TAIL ~ a further arrangement } , the combined cross sectional area is less than 20 % of the cross sectional area of { HEAD ~ the hollow interior }
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD