In The Economist: Seriously, two (2) managers in each position makes a lot of sense.

You need one firm leader. But customers and clients need two folks on each project, no matter how small. Two people need to be available for both questions and a reserve of fresh ideas. But just two. Two project managers, and perhaps one with a “veto power”. See The Economist: “In one’s company, two’s a crowd“. And see our post “The Wonderful Twos“.