I try to duplicate nature as much as is possible in the way I set up the eggs. I have found a lot of clutches of eggs in the wild, but never have I found any in an airtight container. Bear in mind that the eggs are respirating. Intaking oxygen and exhaling carbon dioxide. Granted it's not much, but when the proportion of CO2 to oxygen gets too much, can it harm the eggs? Heck, since even airholes in the tops of my containers allow air in, CO2 is still heavier than air, so will tend to stay in the boxes. But so far I haven't seen any problems I can pin on that as being the cause.
We use pretty much the same ratio for the leopard geckos, but tend to be more in the 1/6 ratio rather than the 1/5 ratio.