#580 shows moulding for column edges. Are two of these getting edge mitered to make a corner? Give me some dimensions and maybe a sketch of the corner.
Basically if you can't get it to butt into the bottom edge of the crown, you have to make a negative of the crown. It only has to be pretty on the surface of the corner and can be hollowed out "roughly" inside. Trace the profile of the crown on both edges of the corner and cut with a coping saw. The cut won't be perpendicular to the face without damaging the other edge. Leave about an 1/8" on both edges and hollow out the middle more than needed - it won't be seen. File the profile to perpendicular and to fit the crown. The top edge should be angled to fit "that" part of the crown. Try this on a scrap piece to get the hang of it.