Well, that's kind of the point. Any design that is intended to be worn at the front is either very small or designed to be moved to the side when it gets in the way of what you're trying to do.

You can wear your backpack as a frontpack if you want to. You'll soon discover why most people don't use them that way. I have done, but only when I have two backpacks to lug some distance and can use the straps of the one worn on the back to help secure the straps of the one worn on the front.