The human ear doesn't really have the ability to determine the height of a source reliably, only left/right. A better effect might be putting the audio out of p

The human ear doesn't really have the ability to determine the height of a source reliably, only left/right. A better effect might be putting the audio out of phase on left/right, which usually has the effect of making it difficult to hear where the sound is coming from (it kind of makes it sound like it's omnidirectional like you mentioned)