Ron, did you ever read any of the UA or Bramwell incubation info? I found a tidbit out that was quite cool and certainly makes sense! actually a few things I didnt know he pointed out in 2012 when I first viewed it.
here is the podcast, someone taped it not so great but its cool to hear his input on incubation!
this is a paste from the Hatching 101 article..... see the purple color font...... read his suggestions below and then the link to the podcast is there as well, I dont think you can view on a cell though. Its pretty long so dont bother to watch until you have time to sit. I did look up some papers on it, and they also made the same conclusions. Whoda thunk!
VENTILATION (OXYGEN)
Ventilation is VERY important during the incubation process.
While the embryo is developing, oxygen enters the egg through the shell and carbon dioxide escapes. Oxygen requirements will increases during development and during hatching. Unobstructed ventilation holes, both above and below the eggs, are essential for proper air exchange. HOWEVER New Studies (Show Dr.Bramwell Discussion) have found that a slight decrease in oxygen the first 10 days (ONLY the first 10) creates a natural higher CO2 level which will naturally build in the incubator and add a little stress to young embryos which will force the embryo to survive and grow stronger, hatch earlier, hatch larger, grow stronger, grow faster and yeild more muscle mass at 6 weeks of age. PUT THE VENT PLUGS IN FOR THE FIRST 10 DAYS ONLY and then REMOVE ALL VENT PLUGS for the rest of the hatch! NOTE: When Lockdown occurs, vent openings are frequently restricted in an attempt to boost incubator humidity. Instead of helping the chick hatch, the chick is suffocated from lack of oxygen. Never decrease ventilation openings at hatching in an attempt to increase humidity. Increase humidity by other methods. If any vent adjustments are made, they should be opened more. Try adding a dampened sponge or towel to help boost humidity during lockdown.
I wonder if elevation would affect this finding - I have read that hatches can be more successful when extra oxygen is added to the atmosphere in the room where the incubator is running, when hatching at higher elevations. I would think plugging the vents would have a negative effect for me.