The vertical center line is usually right on the upper 1/3 part of the fuselage (on the windows or slightly above the windows, depends on aircraft). This way the aircraft looks correctly centered with the rear end (fin) in mind. Do not center the aircraft exactly, like this: space above the fin = space below the gear/fuselage. This is important for side shots; in pic #2-6 it's slighty different. If you want to include the whole fin, crop as tight as possible (leave a few pixels though ) in the upper part, so that the fuselage is in a more centered position.