especially since when you're using sounds you have to find the perfect volume, otherwise it doesnt work and wakes you up.
It's even harder if you consider that your "neurosoup" influences your Sensory Threshold, making your chances even lower. The second aspect is dream integration: you can still incorporate the stimulus in your dream but indirectly: like when you put rose's perfume on your pillow and end up dreaming with a garden. This was studied by an individual some decades ago (he successfully managed to incubate stuff this way) whose name I can't remember.
La Berge studied this theme and found out that the easiest stimulus to integrate is light, but I think the subject is far from settled...Still, this is essentially why the big majority of EILD devices use light cues