AirDrop was always a hit or miss for. I think it's even worse than file shares on Windows which worked me 80% on the time at best.
It seems that the main issue here is peer discovery, but I'm still somewhat astounded nobody has managed to produce an easy-to-use service discovery that works.
Unfortunately AirDrop is two things: a file sharing service over Bluetooth and a file sharing service over wifi. It only recently got somewhat unified which allowed you to use it to transfer files between a Mac and an iPhone but it doesn't seem to be quite ready yet.
Bluetooth is not fast and reliable enough for sharing modern file sizes but there is also no guarantee two phones that are near each other will share a wifi network.
That's the funny thing when specific issue started the discovery worked exactly _one_ way - the MBA would see the iPhone but not the iPhone would refuse to see the MBA. Puzzling at best!
