Avoid the dreaded "Wing Chun Slouch"!!!!

[Kung Fu Wang]

The northern CMA is more open. The southern CMA is more close. IMO, even if you train a pure southern CMA, it can be helpful to add 1 or 2 northern CMA training to balance your posture. If you can just add this posture training into your warm up sequence, it can be helpful and it won't conflict with your WC system.

 

[mook jong man]

I think the main reason for this crappy posture is that they are under the mistaken impression , that to protect your centerline you have to force your elbow in as much as possible.

The only way to do that is to hunch forward so your upper arm clears your lats and your chest , it is just wrong on so many levels.
Early on in their training they probably copped a few fast palm strikes in the chest that slipped past their Fook Sau and thought they were getting through because their elbow was too far out.