Different level, different direction

I was doing some browsing at a few old topics and saw the one about the A/C trains at Nostrand Av having express trains on one level and local on another (also at 59 St/Lex, 86 St/Lex on the 4/5/6 and Bergen St on the F/G [if they ever decide to reinstate express service] and thought about another interesting fact:

There are a number of stations where the downtown trains are on one level and uptown trains are on another level. The one that comes immediately to mind (for me) is 125 St/Lex (4/5/6) with uptown trains on the upper and downtown trains on the lower. None of my reference books have ever addressed a reason for this but I would imagine that space is of the issue.

Other stations I have found with this type of layout. Physical space would be the main issue in that the platforms are stacked rather than on the same level).

Manhattan
Fulton St (on Nassau St - J/Z)
5th Av/53 St (E/M)
7th Av/53 St (B/D/E)
63 St/Lexington Av (F/Q)
72 St (B/C - Central Park West)
81 St (B/C - Central Park West)
86 St (B/C - Central Park West)
96 St (B/C - Central Park West)
103 St (B/C - Central Park West)
125 St/Lex (4/5/6)

Queens
Queensboro Plaza (7/N/W)

Brooklyn
Nostrand Av (3)
Kingston Av (3)
Utica Av (3,4)
Wilson Av (L)

Some might say - what about 14 St and 23 St on the F/M? The uptown and downtown platforms are on the same level. They are placed on either side of the PATH stations on 6 Av.

As to the four B/C stations on Central Park West, I have always assumed that was done because nobody lives in the territory on the east side of CPW; with the usual arrangement, all passengers getting off uptown trains (or boarding uptown trains, for that matter) would be forced to cross auto traffic on CPW. I also like that people working downtown walk down two flights in the morning and climb up one flight coming home -- a minor consideration, but important in those pre-escalator days when the line was built.

I also like that at 7th Avenue on 53rd Street (if I remember correctly, it's been awhile) passengers from Queens going uptown have a cross-platform transfer on the same level while on the return trip they have the same thing on the other level -- no stairs to climb. A similar situation exists at Queensboro Plaza (7/N/W), with one level uptown and the other level downtown. I'd think that from an engineering standpoint it would have been easier to put the 7 on one level and the N and W on the other, but that would have meant lots of passengers crowding the stairs to change trains.

It's been a while for me too but I believe your description of 7th Avenue is correct.

"Back in the day" (actually, back in the Previous Century) a change at 7th was one of my choices to get from Columbus Circle to the Port Authority to make my bus back to Jersey after night school, using the "whatever comes in first" protocol...

Best choice: A express train direct to 42nd/8th Avenue.
Second best choice: C local train direct to 42nd/8th Avenue.
Third best: #1 local to 42nd/Times Square, then walk underground. (If it was pulling in when I got to the station, I took it-- the "whatever comes in first" protocol...)
Fourth best: D train to 7th Avenue, then change to the E train to 42nd/8th.

That was presuming that I didn't walk straight down Ninth Avenue to the Port Authority, which usually resulted in comments like "You walked... and you're not dead?"