This is one of the many methods I use to make myself feel more local. There are some stations where I know precisely where the door is going to stop, but a few I know only a little more vaguely. Then there are the occasions where the conductor stops in a slightly different place because I assume they’re new.
I used to work near a station that was under construction. The only exit was a (shut-off) escalator, while it was a very busy station. I always tried to be the first to be hitting the stairs, and thus after a while, depending on the number of cars (could vary between 3 and
on the train I exactly knew what door to sit next to 
It’s all about the platform. Because all subway platforms are ledges (hollow underneath) and very old they tend to get warn over time. If you look down the length of the platform you can usually make out where the low spots are. That where the most foot traffic has been over the last 70 years or so. Admittedly it’s not an exact science and the trains length varies, but I’ve got about an 80% success rate. The trick is to verify the spacing from dip to dip so they lien up with door distances cause some times there are trick dips
Ooooh, I didn’t even think about that but I’ll pay attention next time I’m on a platform