Have you tested your thermometer? For that matter, did you test your hygrometer to make sure it was reading correctly? This article goes over how to:
https://www.backyardchickens.com/ar...incubator-thermometers-and-hygrometers.73634/ Another way to calibrate your thermometer, if it can read low enough to, is to fill a large measuring cup or bowl with crushed ice and then put just enough cold water in to fill the gaps between the ice. Put your thermometer in there and see if it reads at freezing or not. If you're using a thermometer that can't be submerged, you'll have to put it in a plastic bag and remove as much air as possible before putting it in there, of course. Some thermometers, especially for incubators, don't read low enough to do this with, though.
Yes, the air cell size should be the same in bantam eggs as in large fowl. You're pretty much just looking for the right ratio of air to egg contents, essentially what percentage of the egg is air and what isn't. So the egg is smaller, but the air cell should still look like that chart as far as how big it is compared to the egg as a whole.
Are you setting for the
Easter hatchalong or just coincidental that your eggs arrived when they did? I'll be setting some eggs today, too, though as mentioned earlier I'm not
super confident many will develop.