{HEAD ~ The percentage} of crossover points of the exposed sacrificial fiber channels is preferably {TAIL ~ 25 to 75%, most preferably 30 to 50%} 
is preferably
{ HEAD ~ The percentage } of crossover points of the exposed sacrificial fiber channels is preferably { TAIL ~ 25 to 75 % , most preferably 30 to 50 % }
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL