Hard to mount given no slit in backing sheet

We ordered 5 identical sized rectangular poster wall graphics (24"x18") to be mounted on the same wall. Mounting them so they were all straight and aligned well with each other was very hard given the backing sheets were single sheets. We ended up taking the backing sheets off, cutting them in half, and then putting them back on. It was the only way we could get Overall quality of the printing and product is excellent. I strongly encourage Sticker Mule to consider having a slit in the backing sheets for rectangular prints where it's going to look amateur if not mounted level. They do this if the print >24", but suggest they do for smaller prints too.