Using a rope or bar handle attached to a cable that's set above your head, do a set with an upright torso while standing about 4-5 feet back from the cable column (8-15 reps).
Then do a set with your torso parallel to the floor.
The point of maximal mechanical tension is when your arms form a 90-degree angle to the cable. So, upright torso pulldowns focus more on training you in the shortened to mid-range aspects of shoulder extension. Performing them with your torso parallel to the floor focuses more on the lengthened to mid-range.
It happens every time I write an article or give a workshop. Someone asks me, "So, uh, Dan, do you think I should do it five times a week or should I do it twice a day?" It doesn't matter what "it" is – one arm lifts, Tabata front squats, Olympic lifts–I always get the same perplexing response.