Orientation is important. It is important that the profile be cutin the proper 45 degree orientation. Flip the trim with the top resting on the bed of the miter saw and the bottom facing upward and against the fence. Cut a 45 degree angle to the left of the 0 mark on the saw. The top of the molding should have a strait cut. Cope inward close to the profile and finely sand and true up with a round file. Flip the moulding over and the trim should butt up against the square cut end of the mating piece. This method assume that all inside corners have one coped piece mating agains a piece that is cut square at the end.