But water may pool at the top end of {HEAD ~ the array}, and on {TAIL ~ structures} such as rooftops, the pooling may have undesirable consequences 
But water may pool at the top end of { HEAD ~ the array } , and on { TAIL ~ structures } such as rooftops , the pooling may have undesirable consequences
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH