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