One egg with smaller air sac?

[albinosilver]

Day 14 for my coturnix eggs. I can't see much when candling but I can see the air sac. One egg has a significantly smaller air sac than the others. The others seem all on track. I believe the egg is alive, it seems developed besides the air sac. Does anyone know why this might be?

 

[Rose Quartz]

Day 14 for my coturnix eggs. I can't see much when candling but I can see the air sac. One egg has a significantly smaller air sac than the others. The others seem all on track. I believe the egg is alive, it seems developed besides the air sac. Does anyone know why this might be?

Its possible the shell is thicker, or less porous than the others.