That makes perfect sense. I would love my hair to look on top more like the bottom which is where I tend to have all my volume. Definitely try diffusing upside down using the pixie method (I think thats what its called) and bringing the blowdryer closer to your scalp. Air drying can sometimes weigh down your curls. I recently had a devacut and didn't want to lose length either. I made sure I told the stylist and he was able to fix my ends, shape my hair with layers and still keep length. I did find this video, it says its for thin hair but you can always give it a try and see if it helps. It gave her a good amount of volume with no heat which is a plus.
How To: Voluminous Curls for [FINE/THIN Hair] with NO HEAT! - 3a/3b - YouTube
Good luck experimenting and if you do find something that works please post.