AudioSource IsPlaying confusion

When ever I needed an audio to play I wrote it like this:

if (!sfx.IsPlaying) { sfx.Play(); }

I also have multiple AS on every objects that I want it to make some sounds.

However, the problems lies when I use the above code it prevent any additional sounds when a sound is already playing. Such as, if a BGM is being played from object A and I want object B to do a scream, the scream will never be played.

Also if I just wrote sfx.Play() without the if statement, I got something that sound like a broken record.

So I got an idea that IsPlaying is not being analysed for a single object, but the entire fleet of AS existed in the game. If so, how do I work around this?

Using Unity 5 BTW.