At the gym I use to go to the rear delt machine made actually hitting the rear delts hard. Not sure why. Anyway, on that machine I had to really focus on my elbows being as close to being locked out as possible to really work my rear delts rather than parts of my back. Now at this new gym I go to I find a decent elbow bend is a must to fire up those delts. Only difference between the two is the distance from my body the handles where. So I guess it's just like anything else, just gatta go light and figure out the ideal position to hit your target muscle group. Keep in mind locking any joint out under tension throughout a lift is hard on the joints. Best of luck man!