Are prefabricated crown molding corners supposed to be "flush"?

We are in the midst of a project to put up crown molding in one of our rooms. We purchased the molding AND the prefab inside and outside corners. I thought that cw was supposed to be "flush" even around corners. However, the prefab corners protrude beyond the crown molding pieces that converge at that corner. Believe me, we don't want to rent special equipment and drive ourselves crazy with cutting the molding at the "right" angles for our walls and the molding. I'm OK to use the prefab corners, I just want to make sure that we aren't doing something completely ridiculous. Any guidance would be much appreciated!!