Observations from my Oberengadin 2009 holiday:

• Normal hourly timetable needs three sets in service, leaving Chur at 08 and Arosa at 48 (journey time about 62 minutes).
• Trains cross at Lüen-Castiel and Litzirüti
• Each set consists of a fixed formation of a Ge4/4ii (at the uphill end) and four trailers. Two of the sets are D + A + B + Bt, one set is D + ab + B + abt. The blue “Arosa Express” coaches are enough to make up one set, but are not kept together (the day I was there, one set had the blue D, another the blue Bt and A, whilst the blue B was in the sidings at Arosa).
• Extra passenger coaches or freight are always attached to the rear of the train. For descending trains, this means that the loco ends up in the middle. The most I saw was two coaches or four wagons.
• At Chur, trains arrive in P1, then shunt forward to the yard. Wagons for Arosa are attached to the Chur end by the station pilot, wagons from Arosa are then shunted back into the bays between P2 and the sbb tracks (presumably to be picked up by the pilot and taken across to the RhB side later). The train departs from P2.
• At Arosa, the pattern seems to be similar. I didn’t see which track was used for arrivals, but the wagon brought up from Chur was standing on track 4 with the pilot that had just run round it prior to propelling it to the yard. The train was ready for departure in track 2.