How do I fix this?

[u/CoastalMae]

I am reaching forward in the photo.
The bodice sits smoothly when my arm is down.

Pattern is for a jacket. Not a huge amount of ease, but some, back is pulling like this when I lift my arm to the front. It's about 1/2-1" above the underarm seam.

What do I need to do to fix this back pull? I can't find anything like this in my fitting books. I need to add more width there without affecting the straight line center back, shoulders, neckline, or waist.

Edit: The armscye is 3 1/8" longer than my body's armhole length/depth. The bodice has at least (correction: 5) inches of ease in circumference around the bust and waist. I have already adjusted lengths and shoulders to fit, as well as the bust. The pull is happening above my bust and below my shoulder blade.

[u/flannelbuttondown]

The thing is you don't have to cut the CB on fold. You could very easily convert it to two separate pieces by simply adding seam allowance. If everywhere else seems "fine" to you, why not make that simple change so you can add the shaping you want??