By target backer, do you mean the wooden frame, normally made of 1x2 that has some type of hardboard/cardboard in the top center where your targets are stapled? Looks sort of like this: Click image for larger version.  Name: 51egbRjZBvL._SX425_.jpg  Views: 46  Size: 14.4 KB  ID: 73920

The 1x2 legs go into the PVC in the ground. You then staple or otherwise attach your paper target to the hardboard/cardboard. If the target is sized correctly it can be used at any distance you choose as long as there are PVC pipes in the ground at that distance to place the target stand.