An end effector for a surgical instrument comprises a first jaw and a second jaw. The first jaw is configured to receive a staple cartridge. The second jaw is movable relative to the first jaw and is configured to provide an anvil for forming staples. The anvil has staple forming pockets. Each staple forming pocket comprises first and second staple forming surface regions configured to receive respective first and second staple legs. The first and second staple forming surface regions each have a respective length that is greater than half of the length of the staple forming pocket. The staple forming surface regions may include convex surfaces that drive staple legs laterally. The pocket minimizes re-entry of staple leg tips into tissue.