OpenAL

Hi there

I have been playing around with OpenAL and positional sound, I am using corona sdk

is there are way to make sound, sound like it is coming from behind a player,
if for example if I have a sound positioned at

x:0 and y:10
or
x:0 and y:-10

the sound balance through each of the speakers seems to be the same.

can anyone suggest how I can get a better way to get a better sense of where the sound is emanating from.

Thank you for your help

Mac