Seal stretch concerns

Hey guys I wonder if you could help me with something I've noticed tonight whilst videoing myself doing the seal stretch from behind  . Another seemingly simple stretch yet it has highlighted some obvious issue 

my first video ( first pic) I noticed a very definite discrepancy In upper trap height between each shoulder . So the second video (second pic) I actively tried to correct it (something in the months before I hadn't even thought about could be happening - another example of why we should always film ourself ) incidentally during my seated shoulder flexion in hs1 it had been noted before that I am elevating stronger one side again for what reason,  other than my mind telling me to, im  not sure 

can you advise me what has or is causing this and things maybe I need to take into my training from here on in .

Also I am strongly retracting and pushing tall through my shoulders as coach instructs and am concerned my scaps may be winging (a term I've heard in the past ) but not sure if this is just  muscle showing through so could do with some expert advise here also 

many thanks as always 

Hey Leigh, this situation strongly depends also on your anterior chain. I mean that IF your right side has tight pec minor and lats then the shoulder blade tends to tilt forward and this leads to a slight elevation. when in the seal position try FIRST to externally rotate the upper arm completely and then depress and retract.

Thanks Alex 

ok I will certainly try to ex.rotate first before I do my  depress and retract . 

Do you suggest I work on anything in particular to address this or is it something that just needs my mind being aware of when performing such exercises ???

many thanks