If the bottom ply includes one wall, {HEAD ~ the wall} can be positioned either between {TAIL ~ the top ply inner and outer walls}, or inside of the top ply inner wall 
positioned between
If the bottom ply includes one wall , { HEAD ~ the wall } can be positioned either between { TAIL ~ the top ply inner and outer walls } , or inside of the top ply inner wall
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH