WHO CAN HELP? PASSENGER CAR ROOF

This is one I haven’t been ab;e to solve, despite looking at every picture of a passenger car I have, including web sites- I’m sure I’ve looked at hundreds.

Heavyweight cars were upgraded with airconditionong vents (I think) and this is evident on cars where the clerestory roof is fared over.
Was this done on both sides of the clerestory or just one, or were there different practices?
No photo I have shows this!!
I have an n scale Rivarossi car where the faring is on one side only- is this correct?
Can anyone suggest a good way to duplicate this fairing on models? (n scale)- I was thinking of using putty and sanding to shape- Are there better ideas?
Thanks for any help on this

It was done on one side from most I have seen. The Rivarossi car is correct The duct work only needs to go down one side to service the rooms. Excess cool air vents out through the passage way.

Jim.