I'm sure you're right about adding more reflective layers, but I'm pretty sure that not all reflective layers are equally efficient. The one on a NeoAir is probably not near as efficient as those on emergency blankets, so an emergency blanket under a NeoAir may help keep you a bit warmer, but I'd suspect it wouldn't be much.

It also makes a difference on how close the reflective surface is to your body, so one placed on top of your NeoAir may also help keep you warmer. Since the NeoAir material does not breath, I see little downside in trying it on top of one if you're cold.