Eh, there is no true definition of the Iron Curtain. When the WW2 ended, Yugoslavia was in extremely good relations with the USSR. However, the situation changed in 1948, and Yugoslavia opened to the West. West Germany remained the main trading partner of Yugoslavia until her downfall. Yugoslavia often acted as proxy arms dealer of the US, when the US was unable to trade directly. Things such as Coca Cola and Rock'n'Roll were widespread in Yugoslavia. All that taken together, I think it's safe to say that post-1948 Yugoslavia was not behind the Iron Curtain (at least from the American perspective, but I think you refer to it).