Ideal setting in the longitudinal direction (rear window glass, retractable)

Measure distance (A) from the B-pillar cover (1) to the rear door window glass (3).

Distance (A): 

A = 8 ± 0.8 mm

B = 50 mm from roof frame strip(2)

Fig 1: Identifying Distance Between B-Pillar Cover And Rear Door Window Glass

Courtesy of BMW OF NORTH AMERICA, INC.