Adjusting a sliding patio door: does the door have to rest equally on both rollers?
Moving a roller up or down has a minuscule effect on the load shared by the two wheels. The door's center of gravity will not move more than one-half inch either way. The two wheels will always share the load equally +/- 5%. Wheel replacements are available, or remove the door and oil the pivot points. 

The top or bottom sill can have a dip or a bulge and still read level. Use a string line to check your bottom sill. From your drawing, a dip in the middle of the bottom plate would cause the 2 glass sections to lean toward each other. Set the rollers to achieve parallel between each section, and between the sliding glass and the side frame. If you lower the sliding part, be sure the frame remains in the top track.