If I've got to be honest, I don't think that many board the 0825 EMT service at Stockport towards Manchester. It certainly isn't noticeable through the 4 carriages, not often is there more than 10 standing in the carriage I sit in, 2nd from front in a 4 car set. No hope of getting Hazel Grove passengers on at all if just 2 carriages turns up, never mind Stockport.
If the passengers are evenly distributed that would mean about 40 standing in total so you certainly not almost guaranteed a seat as edwin_m suggested.
There did used to be quite a lot of passengers using that service between Stockport and Manchester Oxford Rd but maybe if they got fed up with EMT only sending 2 cars some of the time they resorted to using other services instead.
From my experience most passengers boarding at Stockport seem to board the 3rd carriage when it's a 4 car formation (unless the 3rd carriage looks very full.) With there being no train length announcements at Stockport (except for Virgin) passengers waiting at Stockport don't tend to spread out along the platform that much (except for XC and Virgin services.)