First Select “View Pose” and adjust shoulder joint. Here I pulled the joint way out so change is visible.
Next “Save Pose” and view reverts to default pose. (but changes are saved)
To view changes, select “View Pose” again. (change is still there)
Now retarget desired animation to adjusted skeleton (Note change still present in skeleton)
Check retargeted animation. Note the change is still present in the retargeted animation.
Finally with your character, instead of pulling shoulder joints way out, pull them out just a little to the desired position following all the steps listed here.
As shown here, you can adjust the shoulders (or any other joint) as much or little as you want.