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