A high reflector is affixed to {HEAD ~ the optics plate} and configured to receive {TAIL ~ the fourth reflected beam} 
A high reflector is affixed to { HEAD ~ the optics plate } and configured to receive { TAIL ~ the fourth reflected beam }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL