Will's point is critical. If your beam needs to resist tension at the joint with the post, then you'll need a healthy end distance (relish) on the tenon. Based on our testing, you need at least 4" on EWP from the center of the peg to the end of the tenon to avoid failure of the tenon. However, if the joint does not need to resist tension, then you need enough bearing on the bottom side of the beam and tenon to carry the beam shear. If you are not sure of how the structure will carry loads, find an engineer to do an analysis. You can get a copy of the EWP test results from the members only section of the web site. Get the "long-term report" by Schmidt and Scholl.