I rode to and from Suffern when it was still Erie Lackawanna but really can't provide a specific answer about the track layout. Sorry. I can say the trains layed over in the middle of the yard, close to the Thruway overpass, you could see your train laying up in the yard (tho just barely as I recall) from the eastbound platform. They seemed to get in and out of the yard fairly easily.
As I think about this I believe that was the turn jobs, that you could see from the eastbound platform (if there was nothing in the way). When they were just about ready to pull down to the station to go east you'd see the headlight come on. The trains that tied up overnight, I think their storage tracks were further west, west of the Thruway overpass. They might've entered those tracks from
the west too.
I can tell you that, though I only go back as far as 1967, the road switchers used to run around the train at Suffern yard. The long end would lead westbound, the short hood would lead eastbound. I never saw them operate a single E unit on a Suffern train, always a pair.
Back in steam days there was a small roundhouse and turntable at Suffern. Near the wye to the Piermont Branch. It shows up on vaulation maps from the 1920s (if you can find one). I got that information, btw, after an inquiry to the Erie Lackawanna Historical Society, of which I am a member.