{HEAD ~ Wafer shaped shields} may occupy {TAIL ~ positions} adjacent top and bottom wafers to cause them to heat the same as other wafers in the rack 
{ HEAD ~ Wafer shaped shields } may occupy { TAIL ~ positions } adjacent top and bottom wafers to cause them to heat the same as other wafers in the rack
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH