If you don't want to use crown with less width (height), then you'll have to run it across the window opening. Since you'll be left with a 5/8" overhang, you might want to attach a piece of flat/s4s moulding to the top of the window opening, between the window and the bottom of crown, to fill the space and provide a finished and intentional look. Play around with it and see how it look.
Personally, I wouldn't run the picture rail into the window opening. I would set my return to end right at the edge of the opening.
Personally, I wouldn't run the picture rail into the window opening. I would set my return to end right at the edge of the opening.