Most people aren't flexible enough in the wrist to hold it olympic style so they go for the arm cross version. Their is another version where you put your arms out at an angle and keep them straight. I prefer that version. Of coarse people could learn the correct version if they worked on wrist flexibility. For posterior delts I do face pulls with a band and if I pull out the hole time I can really feel it in my posterior delts. If you don't have bands I'd imagine you could similate it by doing a bent over barbell row but pulling it to your face. Also it is important to pull outwards on the bar because this will really make you feel it in the real delts.