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