if I am reading this correctly, try placing the crown upside down on the miter saw, with the fence acting like the wall. and make a cut that is 22.5 degrees. cut one end one direction, the mating board the other direction.
you will need to make sure the small flat of the crown is flat against the fence for a good cut.
you will need to make sure the small flat of the crown is flat against the fence for a good cut.
