The biggest problem of a backer at 72" or whatever is the fact that everytime you change targets you would have to tape up the holes or replace the backer for the next shooter. At WWCCA we have a replacement card for the moving backer and the 3 person target crew can change targets, that is pull the existing targets, replace the targets with new ones, and pull the removeable backer, replace the backer card, in 3 to 4 mins and that is on a 18 bench range. If you had 18 benches with a backer system at 72" how long would it take to tape up the holes?? Don't forget 18 X 5 = "90" The "SAD" fact is you have people who will shoot 3 shots and put the other 2 in the dirt, trust me when I tell you this, I have seen it. Secondly some shooters forget how many shots they have actually fired, it happens, is that person trying to cheat?? I don't think so. To end my take on this, moving backers are required.
P.S.
I will be in Little Rock AK for a week or so then back to Detroit for another week, but I will have internet access, I hope!! If you want I will take a bunch of pictures of backer systems here but I think you have more then enough expertise out there.