Movements for the posterior deltoid done in the transverse plane are also referred to by terms like rear delt fly, reverse fly, rear lateral raise, bent-over lateral raises or other variations.
Other muscles such as the lats and middle delts can also come into action, dependent on how the shoulder is rotated.
While leverage is most difficult with fully extended elbows, a slight bend is useful as it allows the lifter to maintain awareness of this.
Some lifters will retract the scapulae and hold them there, as opposed to letting them protract, to get a better stretch in the posterior deltoid.
[2] The arms have the same orientation relative to the ground as in the "shoulder fly" which is done to target the lateral deltoid.
The more the elbow is bent, the more leverage gravity has pull the hand down and turn into a transverse extension angle.
Bodyweight/supine rows (or "australian pullups") can also be done with a wide overhand grip to target the rear delts.
[5] Another option for doing a raise to target the posterior deltoid is hyperextending the glenohumeral joint.
The lat is no longer an extensor at this point, so it is primarily the posterior deltoid and long head of the triceps that perform hyperextension.
The range of motion for this is very limited, most people can't even hyperextend 45 degrees.