I run a standard arca rail on my Foundations. I like the clean and uninterrupted rail for shooting positional with a bag, it lets the gun slide fore/aft on recoil without interruption. Having the full length of the arca rail also gives options for bipod placement which can come in handy on some obstacles, turning what would be a positional shot into a modified prone if you can get the bipod in the right spot. Sometimes will move bipod on the fly in the middle of a stage, slide it forward or backward for the next position or remove it entirely to go from prone to positional.