The crown is too far up the wall by the looks of it. IOW, if you push the crown down the wall, the open joint @ ceiling will close. If you cannot do that, you need to alter the orientation at the saw; the upside-down crown needs to be less on the table, more on the fence; taller, not flatter, if you follow.
I always ascertain the wall/ceiling coordinates of a crown by placing a piece in the angle of a framing square and taking its measure. These dimensions can be drawn onto the ceiling/wall, and used at the saw to make each cut in the same plane.
Casey

Or, you could eliminate that problem altogether by cope cutting one end of the crown. Since most corners are not an exact 90 degrees, you have to 'fuss' with the two angles to get them to fit. Coping one end simply exposes the profile as a sharp cut, which can then be 'tuned' for a seamless fit.

Coping is what I see most pros doing. But even coping is a learned technique. If you continue to have difficulties, you could consider using corner blocks. Then you have all strainght cuts on the crown.

Even if you cope the joint you must have the relationships (wall/ceiling/saw fence/angle)right or the cope will be open in its own way.
Of course, it will be easier to caulk the h3ll out of an open coped joint than that open miter.
Casey

Coping sounds like a more difficult skill to learn than cutting crown, so I'm trying to avoid that. And I don't like the corner blocks because IMO they're for people who can't cut proper miters. (Oh wait, that would be me! :-) I've also become quite skilled at glopping on the caulk (double :-)).

I did ok cutting smaller crown, and had thought I had finally figured it out. This is bigger stuff, and I'm also using a jig I found at Lowe's, so it sounds like I need to do a bit more practice with some scraps getting it set against the fence properly.

Thanks for all your help and suggestions.

And corners are not usually completely square because there is so much tape and drywall mud in a corner and that changes its relationship to the walls on each side of it. As you said--try cutting some scrap first. Experiment not only with changing the angle slightly on your saw, but compounding may help too.

The way I've seen the experts cope crown is to,first, make a 45 degree cut on it. Then cope off the cut following the line between the face of the crown and that 45 degree excess. I'm not an expert at coping---but I do a very fine job of it and the joints are very tight. Why not give it a try? You might have a talent for it. If the piece isn't real long, you can do a fine coping job with a table jigsaw.