Not many people I know who can self tape their backs!
There are over 14 muscles attached to the scapula, and unless one can rotate their head like an owl 180degrees I do not see how a self assessment of the musculature, position, and joint play is possible
During weight training, a good-great muscular balance is required to execute many exercises.
For example, in bench pressing or shoulder pressing movements, I often see people with upward rotation and elevation of the scapulae during these movements. A compensatory pattern is usually seen through the Csp and neck musculature.
How does this affect the AC joint, if that is the area of symptoms?
Well, the various muscles again as mentioned above. A slight change in biomechanics from trapezius may influence the firing pattern of deltoids androtator cuff musculature with the combination of poor posture.
I wouldn't recommend beginning pressing movements with altered biomechanics, as sooner than later a larger issue will become.
As a fitness instructor, physiotherapist, and avid weightlifter myself, it is seen even in so called 'fit' populations a variety of joint issues due to abhorrent lifting technique.
Regards