I found a non glitch way of making a barricade float above another in avalanche shown here: http://www.bungie.net/Forums/posts.aspx?postID=21763393 tell me what you think
Noticed this when I made my map The Assault. They don't sit right on top of each other unless you do the interlocking trick. Makes for cool sniper type bunkers as you say, but use in a competitive map? Camp spot.
Look at the pics on the linked page, no interlocking involved. You just have to line the barricades straight on them.
That's what I said mate. Just setting them on top of each other they leave a gap. If you don't want the gap there you have to interlock them.