The Ra and {HEAD ~ Ra} may preferably provide {TAIL ~ Ra/Ra ratio} of at most 0.8 
preferably provide
The Ra and { HEAD ~ Ra } may preferably provide { TAIL ~ Ra / Ra ratio } of at most 0.8
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH