he tops of the legs are cut on a compound angle ― that is, the saw blade is set at an angle, and it runs across the piece at an angle as well. The magic number is 6 degrees. Make the cuts 6 degrees off square (that is, either 96 degrees or 84 degrees, depending on how you hold the square) with the blade also tilted 6 degrees.
Position the legs against the post tongue and test to see that the leg bottoms are fairly close to 22 inches apart; adjust the angles if needed.
Drill pilot holes and attach the legs to the post top with 2-inch screws.