Air sac half way up inside of egg?????

Hi  

I candled an egg at day 10 today and the air sac is normal, low one side, but the other side rises half way up the egg   .
I can see the veins and the chick's dark shadow, but am worried why the air sac is so high in the egg.

Does anyone know why this is? Is the chick okay?

Any advice will be gratefully recieved  .